Magnetism.

Question 1

What is Magnetic force on a moving charge ?

Answer 1

F= q( V x B)= qVBsin #

Question 2

What are the 3 general paths of a charged particle in uniform charged field ?

Answer 2

If #=0 or 180, path is a straight line.
If #=90 , path is a circle.
For any other #, path is a helix. # is the angle between V and B

Question 3

In magnetism , What is radius r=?

Answer 3

r= mv/qB=P/Bq= √2Km/Bq=√2qVm/Bq

Question 4

In magnetism, What is time period T and ω?

Answer 4

T= 2πm/qB

ω=qB/m

Question 5

In magnetism , What is radius r=?,time period T=? and frequency f=? for a particle in a helical path?

Answer 5

r= mv sin#/qB
T=2πm/qB
f=Bq/2πm

Question 6

What is pitch of a helical path

p=?

Answer 6

p= (v cos #)T=2πmv cos#/qB

Question 7

What is magnetic force due to a current carrying conductor ?

Answer 7

F= i(I x B)= ilBsin #

Here # is the angle between I and B or between direction of current an magnetic field.

Question 8

What is magnetic dipole moment M=?

Answer 8

M= NiA
Every current carrying loop in a magnetic dipole.
Direction of M is perpendicular to the plane of the loop and given by right hand screw law

Question 9

What is force on magnetic dipole due to a uniform magnetic field F=?

Answer 9

F=0

Question 10

What is torque on magnetic dipole due to a uniform magnetic field ?

Answer 10

Torque = M x B= MB sin #

Question 11

What is potential energy U on magnetic dipole due to a uniform magnetic field
U=?

Answer 11

U=-M.B= -MB cos #

Question 12

For magnetic dipole in an uniform magnetic field , what is the condition for unstable equilibrium position of the loop?

Answer 12

#=0 is the unstable equilibrium position of the loop.  
F=0
Torque =0
U=MB( maximum )

Question 13

magnetic field due to a straight wire of finite length B=?

Answer 13

B=μ₀/4π i÷r (sin α± sin β)

Question 14

What is magnetic field B due to a straight wire of uninvited length =?

Answer 14

B=μ₀/2π i/r

Question 15

What is magnetic field B on the axis of a circular loop =?

Answer 15

B= μ₀NiR²÷2(R² + x²)^3/2

Question 16

What is magnetic field B at the centre of circular loop = ?

Answer 16

B= μ₀Ni/2R

Question 17

What is magnetic field B on the axis of a solenoid = ?

Answer 17

B= μ₀ni/2 (cos #1- cos#2)

Question 18

What is magnetic field B at centre of a long solenoid = ?

Answer 18

B = μ₀ni

Question 19

What is magnetic field B at the ends of a long solenoid = ?

Answer 19

B= μ₀ni/2

Question 20

Mathematically , what is ampere’s circuital law ?

Answer 20

∫B .dI = μ₀i( net)

Question 21

What is Force per unit length between two parallel current carrying wires ?

Answer 21

F/l= μ₀/2π x i₁i₂/r
There will be attraction if the currents are in the same direction and if currents re in opposite direction there will be repulsion.

Question 22

What is SI unit of magnetic field ?

Answer 22

Tesla. = 1 Wb/ m^

Question 23

What is Condition for the path of a charged particle in uniform magnetic and uniform electric field to remain unchanged ?

Answer 23

E(electric)+ E(magnetic)= 0 ie

qE + q(V x B)=0 ie E=- (v x E)