thequarkyteacher.files.wordpress.com · Web view2.02understand how the use of insulation, double...

Edexcel ScienceiGCSE Physics

O. Mains Electricity2019-2020

Name:________________Physics Teacher:______________

House CG

Year 10

Specification Checklist

2.01 use the following units: ampere (A), coulomb (C), joule (J), ohm (Ω), second (s), volt (V) and watt (W)

2.04 know and use the relationship between power, current and voltage:

power = current × voltage

P = I × V

and apply the relationship to the selection of appropriate fuses"

2.05 use the relationship between energy transferred, current, voltage and time:

energy transferred = current × voltage × time

E = I × V x t

2.07 explain why a series or parallel circuit is more appropriate for particular applications, including domestic lighting

2.08 understand how the current in a series circuit depends on the applied voltage and the number and nature of other components

2.1 describe the qualitative effect of changing resistance on the current in a circuit

2.14 know that current is the rate of flow of charge

2.16 know that electric current in solid metallic conductors is a flow of negatively charged electrons

2.2 know that: • voltage is the energy transferred per unit charge passed • the volt is a joule per coulomb

2.22 identify common materials which are electrical conductors or insulators, including metals and plastics

2.02 understand how the use of insulation, double insulation, earthing, fuses and circuit breakers protects the device or user in a range of domestic appliances"

2.03 understand why a current in a resistor results in the electrical transfer of energy and an increase in temperature, and how this can be used in a variety of domestic contexts

2.06 know the difference between mains electricity being alternating current (a.c.) and direct current (d.c.) being supplied by a cell or battery

2Mains Electricity – Science (Physics)

Key Definitions

Key Word Image Definition

Alternating Current (a.c.)

Current that repeatedly changes direction. This is what comes out of your plug socket.

Circuit Breaker A switch linked to an electromagnet that performs the same function as a fuse. Can be reset and reused.

Conductor A material that permits electrons to flow freely between particles thus allowing electricity to flow through.

Current The rate of flow of charge. It has the symbol ‘I’ and is measured in Amps (A).

Direct Current (d.c.)

Current that travels in a single direction. This is what is used in batteries and most computers/phones.

Double Insulation

Two layers of plastic insulation. No metal parts on exterior. Does not require an earth wire.

Earth Wire A wire attached to the metal casing of an object. If there is ever electricity in the casing, it travels through the earth wire and causes the fuse to blow.

Fuse A short length of wire designed to melt and break in the event of excessive current.

Insulator A material that does not permit electrons to flow freely between particles, preventing the flow of electricity.

Live Wire The wire that carries electricity into a component. The live wire has the fuse attached to it.

Neutral Wire The wire through which electricity returns to the mains. It completes the circuit from plug to component to plug.

Power (electrical)

The rate of transfer of electrical energy in a component.

Resistance A measure of how hard it is to produce a big current in a circuit.


WATTS

https://www.google.co.uk/url?sa=i&rct=j&q=&esrc=s&source=images&cd=&ved=2ahUKEwiW-tmV94jhAhWjAmMBHeVFBrEQjRx6BAgBEAU&url=https://www.quora.com/What-is-meant-by-an-alternating-current&psig=AOvVaw3aP20DE0cCAsdg-Ni1D526&ust=1552903652680310

https://www.google.co.uk/url?sa=i&rct=j&q=&esrc=s&source=images&cd=&cad=rja&uact=8&ved=2ahUKEwito9ii94jhAhW8DmMBHVO7CpkQjRx6BAgBEAU&url=https://www.iskra.eu/en/Miniature-Circuit-Breakers/Miniature-Circuit-Breaker-RI-50/&psig=AOvVaw0cZ_eAJ2Vzm_sCqOTPxklD&ust=1552903706694594

https://www.google.co.uk/url?sa=i&rct=j&q=&esrc=s&source=images&cd=&cad=rja&uact=8&ved=2ahUKEwjM8pi594jhAhVmxoUKHR9YDy4QjRx6BAgBEAU&url=http://electricalacademia.com/electrical-comparisons/difference-between-ac-current-and-dc-current/&psig=AOvVaw3v9ovBgQ7mKhfFs-CTcx07&ust=1552903754600693

https://www.google.co.uk/url?sa=i&rct=j&q=&esrc=s&source=images&cd=&cad=rja&uact=8&ved=2ahUKEwjs_4nv94jhAhWtxoUKHR-fBwwQjRx6BAgBEAU&url=https://www.aeconline.ae/jeddah-cables-company/thhn-thwn-wire-single-core-cu-pvc-nylon/product.html&psig=AOvVaw3fihyiESQaxyQwAZiHz98I&ust=1552903867573522

1: Current

Component Symbols

How many component symbols can you recall from Shell? Add them to the table below.

[Complete the table in pencil if you are unsure]

Component Name Component Symbol Component Name Component

Symbol

Light Bulb Resistor

Switch Variable Resistor

Wire Fuse

Motor Diode

Voltmeter Light Emitting Diode (LED)

Ammeter Light Dependent Resistor (LDR)

Cell Thermistor

Battery Heater

YOU MUST MEMORISE THESE SYMBOLS!


Learning Outcomes:

1. Define current as the rate of flow of charge.2. Review and recap equations and concepts linked to current from Shell. 3. Describe the difference between a.c. and d.c. current.

Current – Summary Sheet

What is the definition of current?

…………………………………………………………………………………………………………

Symbol: Units:

How would I measure current?

Equipment: Component Symbol

How must this piece of equipment be connected? ……………………………………………

Draw a series circuit in the space below that contains a battery, a resistor and two light bulbs:

Add arrows to show the direction that the current is flowing in.

In what direction does current always flow?

…………………………………………………………………………………………………………

How does current behave in the following types of circuit?

Series

…………………………………..…………………………………..…………………………………..…………………………………..…………………………………..

Parallel

…………………………………..…………………………………..…………………………………..…………………………………..…………………………………..

Complete the information below about the equations you learnt in Shell.

QuanityV - I - R -

UnitV - I - R -

QuantityE - Q - V -

UnitE - Q - V -

QuanityQ - I - t -

UnitQ - I - t -

E=I ×V ×t

QuantityE - I - V - t -

UnitE - I - V - t -


Current: A.C. vs D.C.

Key Ideas

1. Alternating current (a.c.) is current that is constantly changing direction and has a value that increases and decreases over timer.

2. This is the form of the current that we get from the mains. 3. Direction current (d.c.) is current that flows in just one direction and has a constant

value. 4. This is the form of current we get from batteries and cells.


Worksheet – Current

1. Define current. (1)

………………………………………………………………………………………………………

2. For each of the circuit below, add the missing values for current. (3)

3. Complete the questions below using the equations you have just reviewed. You must show all of your working [equation, substitution, solution and units]

a. What is the current when 120C if charge flows through a cell in 20s? (3)

…………………..

b. How long does it take for a current of 1A to transfer 90C of charge? (3)

…………………..

c. Calculate the voltage required to cause a current of 8A to flow through a resistance of 7Ω. (3)

…………………..

d. Calculate the resistance if a voltage of 6V causes a current of 2A. (3)

…………………..


e. How much energy is transferred when 42C flows through a circuit with 230V applied across it? (3)

…………………..

f. What is the charge when 20J of energy is transferred through a lamp with 230V applied across it? (3)

…………………..

g. How much energy is transferred when 3A flows through a resistor for 2 minutes with 230V applied across it? (3)

…………………..

h. What voltage is required for a 6A current to produce 600J of energy in 25s? (3)

…………………..

4. What are the differences between a.c. and d.c. current? (2)

…………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………

5. Give an example of an a.c. supply. (1)

…………………………………………

6. Give an example of a d.c. supply. (1)

…………………………………………

7. In what direction does current flow? (1)

………………………………………………………………………………………………………

Score [ /30]


2: Inside the Plug and the Heating Effect of Current

Knowledge and Understanding QuizUse the knowledge you have gained since Shell to answer the following questions:

1. What is the symbol for current?

……………………………………………………………… (1)

2. What is the equation linking charge, current and time?

………………………………………………………………………………………… (1)

3. Draw the following 4 circuit symbols:

Resistor Voltmeter Thermistor LED

(4)

4. What is the form of an alpha particle?

………………………………………………………………………………………… (2)

5. Give 2 advantages of using a parallel circuit over a series circuit.

…………………………………………………………………………………………

………………………………………………………………………………………… (2)

Score [ /10]


Learning Outcomes:

1. Name the three wires inside and plug and describe their functions2. Describe why current can cause a heating effect in wires. 3. Describe the effect of temperature on the resistance of a wire.

The Plug

Key Ideas

1. A plug (and the cable connected to it) contains three wires; earth wire (green and yellow), the neutral wire (blue) and the live wire (brown).

2. Electrical energy travels through the live wire to the appliance. [It is connected to the fuse]

3. The neutral wire completes the circuit. 4. The earth wire protects the user if there is a fault in the appliance. [It is connected to

the longest pin on the plug]. 5. The three pins on the plug are made of brass to ensure they conduct electricity but

are also strong and sturdy. 6. The earth pin is longest to ensure it makes connection with the mains first. 7. The outside of the cable and the plug are made of an insulating material (plastic).8. STETCH ACTIVITY: Wiring a plug available.


The Heating Affect of Current

Key Ideas

1. The wires in a house are designed to have low resistance. 2. This means that the current can pass through easily and therefore the wires do not

heat up. 3. However, in some appliances we want the metal conductor (also know as heating

elements) to get hotter. For example, in toasters and kettles. 4. Wires that make up heating elements have very high resistance. 5. If a wire has high resistance, the electrons will collide more frequently with the atoms

(metal ions) in the wire. 6. Each time they collide, they transfer energy to the wire. 7. This means that as the current passes through the wire it transfers energy to the

heating element causing it to heat up. 8. If you increase the current in a wire, there are more electrons colliding per second

with the atoms in the wire and so the heating effect larger. 9. This heating effect is also what causes filament lamps to glow. 10. It is worth noting here that as the temperature of a conductor increases, it’s

resistance will also increase11. This is because the atoms in the wire are vibrating more vigorously and so it is

harder for the electrons to flow though as they collide more frequently with the atoms.


Worksheet – The Heating Effect of Current

1. Define current. (1)

…………………………………………………………………………………………………

2. Why does a light bulb glow when it is in a complete circuit? (2)

…………………………………………………………………………………………………

…………………………………………………………………………………………………

…………………………………………………………………………………………………

3. Give an example of an appliance that you would want to heat up as current is passed

through (1)

…………………………………………………………………………………………………

4. Why do wires in homes need to have a low resistance? (2)

…………………………………………………………………………………………………

…………………………………………………………………………………………………

…………………………………………………………………………………………………

5. Is it possible for a wire to melt and break? Explain your answer. (2)

…………………………………………………………………………………………………

…………………………………………………………………………………………………

…………………………………………………………………………………………………

6. Explain why current cause cause a wire to increase in temperature. (4)

…………………………………………………………………………………………………

…………………………………………………………………………………………………

…………………………………………………………………………………………………

…………………………………………………………………………………………………

…………………………………………………………………………………………………

…………………………………………………………………………………………………

Score [ /12]


3: Fuses and Circuit Breakers

Knowledge and Understanding QuizUse the knowledge you gained in the previous lessons and since the start of Shell to answer the following questions.

1. Complete the table below for the wires in a plug

(6)

2. What is alternating current?

………………………………………………………………………………………… (2)

3. An object exerts a force of 540N over an area of 0.42m2. How much pressure does it

create?

(3)

4. In the space below, sketch a circuit connected to a cell which has an LDR and a fuse

in parallel with each other.

(4)

Score [ /15]


Learning Outcomes:

1. Describe how a fuse and circuit breaker work. 2. Give the advantages and disadvantages of using a fuse over a circuit

breaker. 3. Carry out an investigation to determine the rating on an unknown fuse.

Fuses and Circuit Breakers

Key Ideas

1. Fuses and circuit breakers are safety devices that stop the flow of current in a circuit if it becomes too large.

2. This can prevent damage to the device and the user. 3. Fuses contain a small piece of wire with a very low melting point. 4. If current is too high, it heats up the wire in the fuse until it melts, breaking the

circuit and thus stopping the flow of current. 5. Circuit breakers contain trip switches which automatically break the circuit in the

case of high current. These can be reset when the fault is resolved.


O2: Investigation – Rating a Fuse

In this investigation you are going attempt to determine the rating on an unknown fuse.

You will do this by very gradually increasing the currentand observing what happens.

What would you expect to see on the Ammeter when you have surpassed the rating on the fuse?

………………………………………………………………

Apparatus

Using the correct component symbols, sketch the circuit diagram for the above set up. [This will be the set up you are using for this investigation].


Health and Safety Check!

Keep hands dry and make sure all equipment is in good working order

Do not touch the fuse wireduring the experiment

In this investigation the method is written in the questions and will be underlined so it is vital that you work methodically through these.

1. If you were setting this equipment up in a classroom you would start by setting the

variable resistor to maximum resistance. Why is it important to have the variable resistor on maximum resistance when the

investigation starts?

……………………………………………………………………………………………………….

……………………………………………………………………………………………………….

2. In the classroom you would then slowly move the sliding contact of the variable resistor

to reduce its resistance.

What effect will this have on the current?

……………………………………………………………………………………………………….

……………………………………………………………………………………………………….

3. You are going to attempt this investigation using an online simulator. Visit the following

website:

https://phet.colorado.edu/sims/html/circuit-construction-kit-dc/latest/circuit-construction-

kit-dc_en.html

4. Begin by adding a battery to your circuit and setting the voltage on the battery to 0.0V

5. Add a fuse, ammeter and resistor series with the battery.


https://phet.colorado.edu/sims/html/circuit-construction-kit-dc/latest/circuit-construction-kit-dc_en.html

https://phet.colorado.edu/sims/html/circuit-construction-kit-dc/latest/circuit-construction-kit-dc_en.html

6. Slowly increase the voltage on your battery.

Watch the ammeter carefully and note down the highest reading before the fuse ‘blows’

Highest reading on the Ammeter: …………..

How will you know the fuse has blown? Explain you answer.

……………………………………………………………………………………………………….

……………………………………………………………………………………………………….

……………………………………………………………………………………………………….

7. Click on the fuse to see its rating.

What was your fuse rating? ……………….

What was the link between your fuse rating and your answer in Question 6?

……………………………………………………………………………………………………….

……………………………………………………………………………………………………….

……………………………………………………………………………………………………….

8. Suggest a way you could improve this investigation.

……………………………………………………………………………………………………….

……………………………………………………………………………………………………….

Troubleshoot

My fuse has blown and I did not look at the Ammeter!

Solution: Click on the fuse to reset it. Make sure you put your battery back to 0.0V first!


Worksheet – Fuses and Circuit Breakers

1. Draw the circuit symbol for a fuse wire. (1)

2. Explain why the circuit symbol is a good representation of the fuse component. (1)

……………………………………………………………………………………………………….

……………………………………………………………………………………………………….

3. What is the purpose of having a fuse or circuit breaker in a circuit? (2)

……………………………………………………………………………………………………….

……………………………………………………………………………………………………….

4. Explain what effect the fuse has on a circuit when the current in circuit gets too high. (3)

……………………………………………………………………………………………………….

……………………………………………………………………………………………………….

……………………………………………………………………………………………………….

……………………………………………………………………………………………………….

5. Give one disadvantage of using a fuse over a circuit breaker. (1)

……………………………………………………………………………………………………….

……………………………………………………………………………………………………….

6. Give two differences between circuit breakers and fuses. (2)

……………………………………………………………………………………………………….

……………………………………………………………………………………………………….

……………………………………………………………………………………………………….

7. Fuses have difference ratings (1A, 3A, 7A, 13A, etc.). What do the ratings mean? (1)

……………………………………………………………………………………………………….

……………………………………………………………………………………………………….

8. How would you choose the correct fuse for your circuit? (1)

……………………………………………………………………………………………………….

……………………………………………………………………………………………………….


9. Under normal working conditions a kettle as a resistance of 40Ω. It is connected to

mains electricity when has a voltage of 230V.

a. What is the current through the kettle when working under normal conditions? (3)

answer…………….unit…………

b. From the options below, circle an approapriate fuse. (1)

c. Explain your choice. (1)

……………………………………………………………………………………………

……………………………………………………………………………………………

……………………………………………………………………………………………

……………………………………………………………………………………………

10. Describe an investigation to test the rating on a fuse. (5)

[You may draw a labelled diagram in your answer]

……………………………………………………………………………………………………….

……………………………………………………………………………………………………….

……………………………………………………………………………………………………….

……………………………………………………………………………………………………….

……………………………………………………………………………………………………….

……………………………………………………………………………………………………….

……………………………………………………………………………………………………….

……………………………………………………………………………………………………….

……………………………………………………………………………………………………….

……………………………………………………………………………………………………….

……………………………………………………………………………………………………….

Score [ /22]


1A 3A 7A 13A

4: The Earth Wire

Knowledge and Understanding QuizUse the knowledge you have gained in the previous 3 lessons to answer the following questions:

1. What is the symbol for current?

……………………………………………………………… (1)

2. How do we measure voltage in a circuit?

………………………………………………………………………………………… (2)

3. Draw the following 4 circuit symbols:

Variable resistor Ammeter Fuse Motor

(4)

4. An unbalanced force of 6kN is applied to an object of mass 800kg. What acceleration does this cause?

………………………… (3)

5. Give an advantage of using a circuit breaker over a fuse.

…………………………………………………………………………………………

………………………………………………………………………………………… (1)

Score [ /11]


Learning Outcomes:

1. Describe what is meant by ‘double insulated’.2. Describe the purpose of having an earth wire in an appliance. 3. Explain how the earth wire prevents the user from potentially receiving a fatal

electric shock.

The Earth Wire and Double Insulation

Key Points

1. When an appliance has a metal casing, this casing should be connected to the earth wire.

2. If the live wire become damaged or dislodged it can come into contact with the metal casing, causing a potentially fatal electric shock if touched by the user.

3. The earth wire provides a low resistance path for the current. 4. Due to the low resistance, current increases enough to blow the fuse, breaking the

circuit. 5. Some modern appliances are now encased in an extra layer of insulation (usually

plastic). We say they are double insulated. 6. Since insulators do not allow current to flow there is no need for these appliances to

have an earth wire.


Model Answer: The Earth Wire and Double Insulation

Below is an example of the use of the earth wire in electrical safety.

Attempt the question yourself first using the knowledge you have just gained. Make sure you use green pen to add any keyword that you have missed to make

sure you have a model answer.

1. Describe how the earth wire acts as a safety feature in an appliance with a metal casing.

(4)

……………………………………………………………………………………………………………

……………………………………………………………………………………………………………

……………………………………………………………………………………………………………

……………………………………………………………………………………………………………

……………………………………………………………………………………………………………

……………………………………………………………………………………………………………

……………………………………………………………………………………………………………

……………………………………………………………………………………………………………

……………………………………………………………………………………………………………

2. Explain why appliances that are double insulated do not need an earth wire.

(2)

……………………………………………………………………………………………………………

……………………………………………………………………………………………………………

……………………………………………………………………………………………………………

……………………………………………………………………………………………………………

What did you miss the first time around?


Worksheet – Safety in Circuits

1. Draw the symbol for double insulation. (1)

2. What effect does current have on the wire/component it is flowing through? (1)

……………………………………………………………………………………………………….

……………………………………………………………………………………………………….

3. Below is the image of an appliance.

Explain what features are necessary to keep the use safe while using the appliance. (6)

……………………………………………………………………………………………………….

……………………………………………………………………………………………………….

……………………………………………………………………………………………………….

……………………………………………………………………………………………………….

……………………………………………………………………………………………………….

4. Below is the image of another appliance.

Explain why this appliance needs less safety features in the wiring than the appliance in

question 3. (2)

……………………………………………………………………………………………………….

……………………………………………………………………………………………………….

……………………………………………………………………………………………………….

……………………………………………………………………………………………………….

Score [ /10]


5: Power Ratings

Knowledge and Understanding QuizUse the knowledge you gained in the previous lessons and since the start of Shell to answer the following questions.

1. How must an ammeter be connected?

……………………………………………………………… (1)

2. What does it mean when an appliance is ‘double insulated’?

………………………………………………………………………………………… (1)

3. The time base on the oscilloscope trace below is 2ms. What is the frequency of the

signal?

(3)

4. In the space below, sketch a circuit which has a fuse connected to a cell.

Add an ammeter and a voltmeter to the circuit to take measurements of current

through and voltage across the fuse.

(4)

5. What colour is the live wire in a plug?

……………………………………………………………… (1)

Score [ /10]


Learning Outcomes:

1. Understand that all appliances are given power ratings measured in ‘watts’2. Review and use the equation linking power, current and voltage:

P=I ×V3. Describe electrical power as the rate of transfer of electrical energy.

Power

Key Ideas

1. Electrical power measures the rate at which electrical energy is transferred (usually turned into heat).

2. Power, current and voltage are linked in the equationPower=Current×Voltage

3. To use this equation voltage must be measured in ‘Volts’ (V), current must be measured in ‘Amps’ (A) and power must be measured in ‘Watts’ (W).

4. Watts can also be expressed as joules per second (J/s)

Worked Examples:

1. How much power is supplied to a light bulb connected to a 25V supply if a current of

0.2A flows?

2. A new LED has a power of 2.5W. It is connected to a mains supply at 230V. How

much current flows through the bulb?


Calculations Worksheet – Power, Current and Voltage

Complete the questions below using the equation you have just learnt. You must show all of your working [equation, substitution, solution and units]

1. Calculate the power of an electric fire that requires a current of 5A for a voltage of 230V.

…………………..

2. Calculate the power of a television that requires a current of 6A for a voltage of 230V.

…………………..

3. Calculate the current drawn when a microwave of power 690W is connected to a 230V supply.

…………………..

4. Calculate the current drawn when a kettle of power 2kW is connected to a 230V supply.

…………………..

5. Calculate the voltage required by an electric fire of power 2.3kW and current 15A.

…………………..

6. Calculate the voltage required by a light bulb of power 24W and current 2mA.

…………………..

7. Calculate the current drawn when a cooker of power 4 MW is connected to a 230V supply.

…………………..

8. Calculate the power when a cooker draws 6mA of current from a 230V supply.

…………………..


Worksheet – Power Ratings, Energy and Safety

You may use the equation below from Shell (given in exam) in the following worksheet.

E=I ×V ×t

1.The table shows information about three electrical appliances.

(a) (i) State the relationship between power, current and voltage.

(1)

(ii) Calculate the current in the television.[assume that the mains voltage is 230 V]

(2)

current = ........................................................... A

(b) The photographs show the different cables used for the clothes iron and the lamp.

(i) Suggest why the wires in the clothes iron cable are thicker than the wires in the lamp cable.

(1) .............................................................................................................................................

.............................................................................................................................................

(ii) The clothes iron cable has three wires, E, N and L.Which of these wires is connected to the fuse?

(1) .............................................................................................................................................


(iii) Suggest why the lamp is safe to use, even though its cable only has two wires.(1)

.............................................................................................................................................

.............................................................................................................................................

(c) The lamp is switched on for 55 minutes.

Calculate the energy transferred by the lamp in this time.(3)

energy transferred = ........................................................... J

2. The photograph shows an extension cable on a reel.

There is a warning label on the reel.

(a) (i) State the equation linking power, current and voltage.(1)


(ii) Complete the table by inserting the missing value.(1)

(b) The extension cable is fitted with a 13 A fuse.

(i) Describe how the fuse protects the cable.(3)

.............................................................................................................................................

.............................................................................................................................................

.............................................................................................................................................

.............................................................................................................................................

.............................................................................................................................................

(ii) Explain why a 5 A fuse is not suitable for this extension cable.(2)

.............................................................................................................................................

.............................................................................................................................................

.............................................................................................................................................

(iii) Suggest why the maximum recommended current is lower when the cable is coiled up.

(1)

.............................................................................................................................................

.............................................................................................................................................

Score [ /17]


STRETCH WORKSHEET : Wiring plugs

Complete the table below, identifying why each plug is unsafe and explaining what can be done to fix it.

PLUG Why is it unsafe? What needs to be done?


STRETCH ACTIVITY – Paying for Electricity

When we pay for the electricity in our homes we are charged by how much Energy we use in kilowatt hours [kWh]. 1kWh is the energy transferred when a 1kW device is used for 1 hour. This can be calculated using the following equation:

Use the equation to complete the table to find out the cost of running each of the appliances below.

Appliance Power Time usedUnits of

electricity /kWh

Cost /p

A CD player 0.03 kW 120 minutes

B Laptop 4 hours 0.3

C Dishwasher 1500 W 1.5

D Iron 1 kW 30 minutes

E Microwave 1.5 kW 0.15

F Washing machine

500 W 90 minutes

G Toaster 15 minutes 0.4

H Fridge freezer 540 W 12.96

I TV 3.5 hours 0.49


Mains Electricity

Past Paper Questions

Q1. A washing machine has an electric motor and an electric heater.


The resistance of the heater is 22 Ω.

The mains voltage is 230 V.

(a) (i) State the equation linking voltage, current and resistance.(1)

(ii) Show that the current in the heater is about 10 A when it is working.(2)

(b) The washing machine is fitted with a fuse rated at 13 A.(i) Explain why the washing machine is fitted with a fuse.

(2) .............................................................................................................................................

.............................................................................................................................................

.............................................................................................................................................

............................................................................................................................................


.

.............................................................................................................................................

(ii) When the motor is working, the current in it is 1.74 A.Explain why it would not be sensible to replace the 13 A fuse with a 2 A fuse.

(2) .............................................................................................................................................

.............................................................................................................................................

.............................................................................................................................................

.............................................................................................................................................

.............................................................................................................................................

(Total for question = 7 marks)

Q2. (a) The diagram shows some electrical circuit symbols.

(i) Which symbol represents a switch?(1)

A

B

C

D

(ii) Which symbol represents a diode?(1)

A

B


C

D

(b) A hairdryer connected to the mains supply takes a current of 5.5 A.(i) Which of these fuses should be used with the hairdryer?

(1)

A 3 A

B 5 A

C 7 A

D 13 A

(ii) Explain your answer.(1)

............................................................................................................................................

.

............................................................................................................................................

.

............................................................................................................................................

.

(iii) The hairdryer has a plastic case so there is no need for an earth wire connection

in the plug.

Explain why the hairdryer is still safe to use.

(2)

............................................................................................................................................

.

............................................................................................................................................

.

............................................................................................................................................

.

............................................................................................................................................


.

............................................................................................................................................

.

............................................................................................................................................

.



Q3. The diagram shows some lamps connected together.

There are 20 small lamps connected in series with a 9 V supply.

(a) (i) What is the voltage across each lamp in the series circuit?(1)

.............................................................................................................................................

(ii) Each lamp has a power of 1.5 W.State the equation linking power, current and voltage.

(1)

(iii) Show that the current in the circuit is about 3 A.(2)

(b) (i) The lamps are on for 7 hours a day for 5 days.Calculate the total energy transferred during this time.

(3)


energy transferred = .............................. J

(ii) Describe the energy changes that take place in the lamps when they are connected to the power supply.

(2)

.............................................................................................................................................

.............................................................................................................................................

.............................................................................................................................................

.............................................................................................................................................


Q4. The diagram shows the lighting circuit in an office.

(a) (i) State two advantages of connecting lamps in parallel rather than in series.

(2)1 ..........................................................................................................................................

.............................................................................................................................................

2 ..........................................................................................................................................

.............................................................................................................................................

(ii) What is the purpose of the 5 A fuse?(1)

.............................................................................................................................................

.............................................................................................................................................


(iii) Explain how a fuse works.(3)

.............................................................................................................................................

.............................................................................................................................................

.............................................................................................................................................

.............................................................................................................................................

.............................................................................................................................................

.............................................................................................................................................

(b) A label on one of the office computers includes this information.

(i) State the equation linking power, current and voltage.(1)

(ii) Use the information on the label to calculate the current in the computer.(3)

current = ........................................................... A

(iii) Fuses are available with values of 1 A, 3 A, 10 A and 13 A.Suggest the most suitable fuse value for the computer.Give a reason for your answer.

(2)fuse value ........................................................... A

reason

.............................................................................................................................................

.............................................................................................................................................


(iv) Some circuits use a circuit breaker instead of a fuse.State two advantages of using a circuit breaker instead of a fuse.

(2)1 ..........................................................................................................................................

.............................................................................................................................................

2 ..........................................................................................................................................

.............................................................................................................................................

(c) The graphs show some ways that power (P) can vary with voltage (V).

Which is the correct graph for a fixed resistor?(1)



Mains Electricity

Spec Point Notes


Specification Notes – Mains Electricity

2.01 use the following units: ampere (A), coulomb (C), joule (J), ohm (Ω), second (s),

volt (V) and watt (W)

2.04 know and use the relationship between power, current and voltage:

power = current × voltage

P = I × V

and apply the relationship to the selection of appropriate fuses


2.05 use the relationship between energy transferred, current, voltage and time:

energy transferred = current × voltage × time

E = I × V x t

2.07 explain why a series or parallel circuit is more appropriate for particular applications, including domestic lighting

2.08 understand how the current in a series circuit depends on the applied voltage and the number and nature of other components

2.10 describe the qualitative effect of changing resistance on the current in a circuit


2.11 describe the qualitative variation of resistance of light-dependent resistors (LDRs)

with illumination and thermistors with temperature

2.14 know that current is the rate of flow of charge

2.16 know that electric current in solid metallic conductors is a flow of negatively charged electrons

[See 2.14]


2.20 know that:

• voltage is the energy transferred per unit charge passed

• the volt is a joule per coulomb

2.22 identify common materials which are electrical conductors or insulators,

including metals and plastics

2.02 understand how the use of insulation, double insulation, earthing, fuses and circuit breakers protects the device or user in a range of domestic appliances


2.03 understand why a current in a resistor results in the electrical transfer of energy and an increase in temperature, and how this can be used in a variety of domestic contexts


2.06 know the difference between mains electricity being alternating current (a.c.) and direct current (d.c.) being supplied by a cell or battery


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