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Daily Practice Problems
Class 12 Physics
Moving Charges and Magnetism

Question 1:

Two parallel wires in free space are 10 cm apart and each carries a current of 10 A in the same direction. The force exerted by one wire on the other (per metre length) is:

1. 2 × 10-4 N
2. 2 × 10-7 N
3. 2 × 104 N
4. 2 × 10-7 N

Question 2:

The current sensitivity of moving coil galvanometer depends on:

(a) number of turns in the coil

(b) moment of inertia in the coil

(c) current sent through galvanometer

(d) eddy current

Question 3:

An electron moving with a speed of 108 m/s enters a magnetic field of 5× 10-3 T in a direction perpendicular to the field. Calculate the radius of the path?

(a) 0.171 m

(b)1.13 × 10-1 m

(c) 1.4 × 103 m

(d) None

Question 4:

Write the expression for Lorentz magnetic force on a particle of charge ‘q’ moving with velocity v in magnetic field B. Work done is:

(a) maximum

(b) W=0

(c) least

(d) none of these

Question 5:

Time period of a charged particle undergoing a circular motion in a uniform magnetic field is independent of:

(a) speed of the particle

(b) mass of the particle

(c) charge of the particle

(d) magnetic field

Question 6:

A straight wire of length 50 cm carrying a current of 2.5 A is suspended in mid-air by a uniform vertical magnetic field of 0.5 T. The mass of the wire is (g= 10m/s2)

(a) 100 g

(b) 125 g

(c) 62.5 g

(d) 250 g

Question 8:

A charged particle enters the uniform magnetic field and experiences an upward force as indicated in the figure. What is the charge sign on the particle?

(a) Neutral

(b) Negative

(c) May be (a) or (b)

(d) positive

Question 9:

A beam of alpha particles and of the protons of the same velocity V, enter a uniform magnetic field at right angles to the field lines. The particles describe circular paths. What is the ratio of the radii of these two circles?

(a) 1:2

(b) 2:1

(c) 3:4

(d) 5:6

Question 10:

Galvanometer is converted to ammeter by connecting:

(a) small resistance in parallel

(b) large resistance in parallel

(c) small resistance in series

(d) large resistance in series

Question 11:

The coil of galvanometer has a resistance of 100 Ω. It gives full scale deflection for a current of 5×10-4 A. what is the value of resistance needed to convert it into a voltmeter to read a maximum potential difference of 5V.

Question 11:

A cyclotron’s oscillator frequency is 10 MHz. What should be the operating magnetic field for accelerating protons? If the radius of its ‘dees’ is 60 cm, what is the kinetic energy (in MeV) of the proton beam produced by the accelerator. (e =1.60 × 10–19 C, mp = 1.67 × 10–27 kg, 1 MeV = 1.6 × 10–13 J).

Question 12:

An element ∆l = ∆x iˆ is placed at the origin and carries a large current I = 10 A. What is the magnetic field on the y-axis at a distance of 0.5 m. ∆x = 1 cm?

Question 13:

A solenoid of length 0.5 m has a radius of 1 cm and is made up of 500 turns. It carries a current of 5 A. What is the magnitude of the magnetic field inside the solenoid?

Question 14:

The horizontal component of the earth’s magnetic field at a certain place is 3.0 ×10–5 T and the direction of the field is from the geographic south to the geographic north. A very long straight conductor is carrying a steady current of 1A. What is the force per unit length on it when it is placed on a horizontal table and the direction of the current is (a) east to west; (b) south to north?

Question 15:

A current-carrying circular loop is located in a uniform external magnetic field. If the loop is free to turn, what is its orientation of stable equilibrium? Show that in this orientation, the flux of the total field (external field + field produced by the loop) is maximum.

Question 16:

Why should the spring/suspension wire in a moving coil galvanometer have low torsional constant?

Question 17:

(a) In what respect is a toroid different from a solenoid? Draw and compare the pattern of the magnetic field lines in the two cases.

(b) How is the magnetic field inside a given solenoid made strong?

Question 18:

State Biot-savart law.

Question 19:

Consider a tightly wound 100 turn coil of radius 10 cm, carrying a current of 1 What is the magnitude of the magnetic field at the centre of the coil?

Question 20:

What are the similarities between Biot-savart law and Coloumb’s law.

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