Jurong Junior College /2011 H1 Physics 8866 10. Electromagnetism

JURONG JUNIOR COLLEGE J2 H1 Physics (2011)

Tutorial: Electromagnetism

Learning Outcomes

Sub-topic Tutorial Questions

a show an appreciation that a force might act on a current carrying conductor placed in a magnetic field.

b recall and solve problems using the equation F = BIL sin θ,with directions as interpreted by Fleming’s left hand rule. 1, 2, 3, 4, 5(a,c), 7, 8

c define magnetic flux density and the tesla

d show an understanding of how the force on a current carrying conductor can be used to measure the flux density of a magnetic field using a current balance

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e predict the direction of a force on a charge moving in a magnetic field 6a,

f sketch flux patterns due to a long straight wire, a flat circular coil and a long solenoid.

Right Hand Grip Rule 7, 8 g show an understanding that the field due to a solenoid

may be influenced by the presence of a ferrous core.

h explain the forces between current carrying conductor and predict the direction of the forces.

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(A) Force on a Current Carrying Conductor 07JJ/P1/30 1. The diagram shows a current-carrying conductor RS of length 2 m placed perpendicularly

to a magnetic field of flux density 0.5 T. The resulting force on the conductor is 1 N acting into the plane of the paper.

What is the magnitude and direction of the current?

A 1 A from R to S B 1 A from S to R C 2 A from R to S D 2 A from S to R

S

2 m

R

0.5 T

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Jurong Junior College /2011 H1 Physics 8866 10. Electromagnetism

07HC/P1/30 2. A bent wire PQRST carrying a current I is placed in a magnetic field of flux density B as

shown. QR is 16 cm in length and RS is 30 cm in length. PQ is shorter than ST.

Using the notation Fxy to represent the magnitude of the force experienced by a segment

XY of the wire due to the magnetic field, which of the following is true? A FQR ≠ FRS and FPQ < FST B FQR = FRS and FPQ = FST C FQR > FRS and FPQ < FST D FQR < FRS and FPQ = FST 07IJ/P1/24 3. A straight wire PQ carrying a constant current I is placed at right angles to a uniform

magnetic field, as shown by the dotted line in the diagram.

The wire is then rotated through an angle θ about an axis perpendicular to the plane of

the diagram. Which graph shows how the magnitude of the magnetic force F on the wire varies with θ in the range 0o to 90o?

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Jurong Junior College /2011 H1 Physics 8866 10. Electromagnetism

07/SRJC/P1/ 34 4. A current balance device as shown in figure below was set up to determine the magnetic

field strength created by a solenoid. The first experiment determined the magnetic field strength as B. The setup was used again with one or some of the factors changed. A larger mass of the rider had to be used in the second experiment.

Which one of the following could most likely be the changes made? A The knife edge was moved closer to PQ B The current passing through the solenoid and the number of turns of the solenoid

are reduced C The first experiment was set up such that the direction of the Earth’s magnetic field

is opposite to the magnetic field created by the coil while the second experiment had both magnetic fields in the same direction.

D Another frame with a shorter length for PQ was used N99/II/4 5. A metal wire of length 0.57 m and cross-sectional area 1.0 x 10-6 m2 is situated at right

angles to a uniform magnetic field of flux density 1.8 x 10-3 T as shown below.

The metal of the wire has density 7.9 x 103 kg m-3 and resisitivity 8.8 x 10-8 Ω m.

A potential difference is applied between the ends of the wire so that there is an electromagnetic force acting on the wire.

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Jurong Junior College /2011 H1 Physics 8866 10. Electromagnetism

(a) Mark the direction of the current in the wire on the above figure (b) For the wire, calculate (i) its weight [0.044 N]

(ii) its resistance [0.050 Ω]

(c) Calculate the potential difference required between the ends of the wire for the

electromagnetic force on the wire to equal its weight. [2.14 V]

(d) The horizontal component of the Earth’s magnetic field is 1.8 x 10-5 T. State and

explain why, in practice, current carrying wires are not seen to lift off the ground.

N88/III/10 6. A U-tube of uniform square cross-section has electrodes sealed inside the upper and

lower walls of the horizontal section, the two arms of the tube being vertical as shown below. The tube is partially filled with liquid sodium and a direct current is passed between the electrodes. A uniform horizontal magnetic flux is to be applied to the horizontal section of the tube in a direction normal to the vertical plane containing the tube.

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Jurong Junior College /2011 H1 Physics 8866 10. Electromagnetism

(a) With the aid of a diagram, explain why the level of the liquid in the two vertical arms of the tube will change on application of the field.

(b) Calculate the difference between the heights of the liquid levels given that

the area of cross-section of the tube = 1.2 x 10-4 m2 the current between the electrodes = 5.0 A, the magnetic flux density = 0.20 T, the density of liquid sodium = 900 kg m-3 [10.4 x 10-3 m]

(c) Discuss the effect of increasing the area of the electrodes within the region of the

magnetic flux on the difference in the vertical heights of the liquid levels. Assume that the current is supplied from a d.c. source of constant e.m.f. and negligible internal resistance.

(C) Force between current-carrying conductors 07AJC/P1/30 7. A long, horizontal, straight wire is placed close and parallel to the plane of a coil as

shown in the diagram. Both the coil and the wire carry currents I1 and I2 respectively in the directions indicated.

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Jurong Junior College /2011 H1 Physics 8866 10. Electromagnetism

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The force at point P on the wire due to these currents is A in the direction of X. B in the direction of Y. C out of the plane of the paper. D into the plane of the paper. 07/MJC/P1/27 8. A coil carries a current in an anti-clockwise direction while a wire

located at the axis of the coil carries a current that is coming out of the paper, as shown below. What is the effect of this set-up on the coil?

A It does not experience any magnetic force. B The resultant force on the coil is zero. C It experiences an attractive force towards the centre. D It experiences a repulsive force away from the centre. 07RJ/P1/ 28 9. Six vertical conductors are placed at the corners of a regular hexagon ABCDEF as shown

below. Each conductor at A, B, C, D and E carries equal currents in the same direction perpendicular to the plane of the paper. The conductor at F carries the same current but in the opposite direction.

Ignoring the Earth’s magnetic field, in which direction is the net force on the conductor at C due to the other conductors?

A North B South C East D West

END

A

DE

F C

B

EastWest

South

North