Physics -Trial Semester 2

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Section A [15 marks]
Answer all questions in this section

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Section B [15 marks]
Answer all questions in this section

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Section C [30 marks]

Answer any two questions in this section

18 (a) Explain the mechanism of electrical conduction in a conductor when it is connected to

a battery. [3 marks]

(b) A potential difference of 2.0 V is applied across a metal wire of length 24 cm and

cross-sectional area 5.03 x 10-3 cm2. A current of 1.5 A is produced.

(i) Determine the electric conductivity of the wire. [3 marks]

(ii) The mean free time between collision of free electrons with atoms is 1.78 x 10-15 s.

Determine the number of free electrons per unit volume. [2 marks]

(iii)Calculate the drift speed for the free electrons. [2 marks]

(iv)The typical speed of free electrons in a solid is in the order of 106 m s-1. Explain

the difference between typical speed and the drift speed in (b)(iii). [2 marks]

(c) Explain how the electric conductivity of a conductor depends on the change of

temperture. [3 marks]

19. (a) Explain the difference between the terms electromotive force and potential

difference. [2 marks]

(b) State Kirchhoff’s first law and Kirchhoff’s second law. [2 marks]

(c) The circuit diagram below shows a circuit containing batteries and resistors.

You may assume that the batteries have negligible internal resistance.

ε1

1.25 A 6Ω 10 Ω

0.5 A 5Ω

ε2
(i) Use Kirchhoff’s first law to find the current flowing through the 6.0 Ω and 10.0 Ω

resistors.

(ii) Calculate the e.m.f. of ε1. [2 marks]

(iii) Calculate the e.m.f. of ε2 [2 marks]

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(d) The circuit diagram below shows a potentiometer circuit. A driver cell of e.m.f. 4.0 V is
connected across a 1.0 m length of resistance wire.

4.0 V

A C
B

G

ε

A cell of unknown e.m.f. ε, is connected to the potentiometer at A and to a jockey which makes

contact with the resistance wire at C. A balance is obtained when the length of AC is 35.0 cm.

(i) Estimate the value of ε. Explain why this can be only an estimate. [3 marks]

(ii) A standard cell of e.m.f. 1.18 V gives a balance length of 30.2 cm. Use this value to

obtain a more accurate value for ε. [4 marks]

20 (a) A charged particle passing through a region of magnetic field moves in a straight line.

State the direction of the magnetic field with respect to the motion of the particle.

Explain your answer. [3 marks]

(b) A proton moves in a circular path perpendicular to a constant magnetic field strength
of 4.0 x 10-3 T. If the momentum of the proton is 1.52 x 10-23 kg m s-1, determine

(i) the radius of the circular path, [4 marks]

(ii) the speed of the proton. [2 marks]

(c) A solenoid has 25 turns per cm, and carries a current of 5.00 mA. An electron inside
the solenoid moves in a circular path with a speed of 1.50 x 105 m s-1.

(i) Determine the magnetic field strength in the solenoid. [2 marks]

(ii) Determine the magnetic force on the electron. State the reason why the force does

not increase the kinetic energy of the electron. [2 marks]

(iii) Sketch a vector diagram to show the direction of the velocity v, the magnetic field

B and the magnetic force F for the electron. [2 marks]

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