Moving Charges and Magnetism

Question 1

direction of Lorentz Magnetic Force can be determined by

Answer 1

Fleming’s left hand rule

Question 2

frequency of motion of charged particle in uniform magnetic field is

Answer 2

gyrofrequency or cyclotron frequency

Question 3

Gyrofrequency is independent of

Answer 3

V ie speed

Question 4

Pitch of helix

Answer 4

Linear distance travelled by charged particle in the direction of M.F during one rotation

Question 5

T =

Answer 5

2πm/qB

Question 6

Pitch =

Answer 6

VcosθT

Question 7

E/B ratio is called

Answer 7

Velocity Selector

Question 8

Biot savart’s law

Answer 8

Magnitude of MF is prop to I, current element dl, sinθ and inversely prop to r^2

Question 9

Similarities & differences of Biot-Savart’s law with Coulomb’s law

Answer 9

1. Both are of long range, both depend inversely on square of distance
2. Principle of superposition applies to both
3. E.F is produced by a scalar source but MF by vector source
4. EF is along displacement vector joining source & field point. MF is perp to plane containing displacement vector r and dl
5. There is angle dependence in Biot’s law which is not there in other
6. MF at any point in the direction of dl is 0.

Question 10

Applications of Biot Savart’s law

Answer 10

Calculate the magnetic field in various positions with respect to the current-carrying conductor

Question 11

Ampere’s Circuital law

Answer 11

Line integral of MF on any closed path is equal to μo times total current passing through it.
If B is directed along the tangent to every point on the perimeter L of a closed curve, its magnitude is same at all points

Question 12

What is 1A current?

Answer 12

Steady current which when maintained in each of two very long straight || conductors of negligible cross section, placed unit dist apart in vacuum would produce force of 2/10^7 /Nm on each.

Question 13

Why can galvanometer not be used as ammeter?

Answer 13

Galvanometer is very sensitive device. It gives full scale deflection for current
Since it has high resistance, it will change the value of I. So shunt resistance is needed in || with the coil

Question 14

Current sensitivity can be increased by?

Answer 14

More no of turns
Using strong magnet
Increasing area of coil
decreasing torsional constant k

Question 15

_______ is used to make MF radial & increase strength of MF

Answer 15

Soft iron core

Question 16

Why does Voltage not increase when no. of turns increase?

Answer 16

Due to R

Question 17

Ideal voltmeter has __________ resistance

Answer 17

infinite