View all 25 cards in this deck

#	Question	Answer
1	Does the magnetic force do work on a charged particle?	No. The magnetic force is always perpendicular to the velocity.
2	What is the magnitude of the magnetic force on a charged particle?	\( F = q v B \sin\theta \).
3	What is the angular frequency of a charged particle's circular motion in a magnetic field?	\( \omega = \frac{qB}{m} \).
4	What is 1 gauss in tesla?	\( 10^{-4} \) T.
5	What is the magnetic field at the centre of a circular loop carrying current \( I \)?	\( B = \frac{\mu_0 I}{2R} \).
6	An element \( \Delta\mathbf{l} = \Delta x \hat{i} \) at the origin carries a current of 10 A. What is the magnetic field on the y-axis at 0.5 m? (\( \Delta x = 1 \) cm)	\( 4 \times 10^{-8} \) T in the +z direction.
7	A tightly wound 100 turn coil of radius 10 cm carries a current of 1 A. What is the magnetic field at the centre?	\( 6.28 \times 10^{-4} \) T.
8	Do the straight segments of a semicircular wire contribute to the magnetic field at the centre?	No.
9	What is the magnetic field inside a long solenoid?	\( B = \mu_0 n I \).
10	How does the magnetic field vary with distance inside a current-carrying wire?	Directly proportional to the distance from the axis.
11	What is the definition of the ampere?	The steady current which, when maintained in each of two long parallel conductors placed 1 m apart in vacuum, produces a force of \( 2 \times 10^{-7} \) N per metre of length.
12	What is the force on a wire carrying current from south to north in the earth's magnetic field?	Zero.
13	When is the torque on a current loop zero?	When the plane of the loop is perpendicular to the magnetic field (\( \theta = 0^\circ \)).
14	A coil with magnetic moment 10 A m² is placed in a magnetic field of 2 T. What is the torque when the coil has rotated by 90°?	20 N m.
15	How is a galvanometer converted into a voltmeter?	By connecting a high resistance in series with it.
16	Is a current loop equivalent to a magnetic dipole?	Yes, at large distances.
17	What is the torque on a current loop?	\( \boldsymbol{\tau} = \mathbf{m} \times \mathbf{B} \).
18	A closely wound solenoid 80 cm long has 5 layers of 400 turns each and carries 8 A. What is the magnetic field inside?	\( 2.5 \times 10^{-2} \) T.
19	What is the magnetic field 1.5 m below a horizontal power line carrying 90 A from east to west?	\( 1.2 \times 10^{-5} \) T (southward).
20	What kind of source produces the electrostatic field, and what kind produces the magnetic field?	The electrostatic field is produced by a scalar source (electric charge); the magnetic field is produced by a vector source (the current element \( Id\mathbf{l} \)).
21	A flexible, irregularly-shaped current loop sits in an external magnetic field. Why does it tend to reshape itself into a circle?	To maximise the flux through it — for a given perimeter, a circle encloses the greatest possible area of any shape, and the loop naturally orients and deforms to maximise flux.
22	If the number of turns N in a galvanometer coil is doubled, what happens to its current sensitivity and its voltage sensitivity?	Current sensitivity doubles (it's proportional to N). Voltage sensitivity stays unchanged, because the coil's resistance R also roughly doubles (being proportional to wire length), and voltage sensitivity depends on N/R.
23	What is the approximate magnitude of the Earth's magnetic field?	About \( 3.6 \times 10^{-5} \) T.
24	For the same two moving coil meters, what is the ratio of voltage sensitivity of \( M_2 \) to \( M_1 \)?	1 (equal voltage sensitivity).
25	A galvanometer of resistance 100 Ω gives full-scale deflection for a current of 1 mA. What shunt resistance converts it into an ammeter reading up to 1 A?	≈ 0.1 Ω — from \( r_s = \frac{I_g G}{I - I_g} = \frac{0.001 \times 100}{1 - 0.001} \), using the fact that the galvanometer and shunt carry the same voltage (Ohm's law on the parallel combination), the same principle used in Example 4.12.