Electromagnetism

Question 1

What is magnetic field?

Answer 1

It is the region of space where a magnetic pole, moving charged particle or current-carrying conductor will experience a magnetic force

Question 2

How to find direction of magnetic field at a point?

Answer 2

Tangent to a field line or curve at a point

Question 3

What is the strength of magnetic field indicated by?

Answer 3

Density of magnetic field lines
- magnetic field lines close together –> stronger
- magnetic field lines further apart –> weaker

Question 4

What direction do magnetic field lines point in?

Answer 4

Away from North towards South pole

Question 5

How to tell if magnetic field is uniform?

Answer 5

Lines of force are parallel

Question 6

Why do magnetic field lines not intersect?

Answer 6

There can only be one direction for field at any point

Question 7

How do magnetic field differ from electric field?

Answer 7

Magnetic field only acts on moving charges while electric field is produced by static charges

Question 8

What does a dot represent?

Answer 8

Coming out of the page

Question 9

What does a cross represent?

Answer 9

Going in the page

Question 10

What is magnetic flux pattern of current carrying conductor?

Answer 10

Concentric circles, radiating outwards with increasing radius

Question 11

How to determine direction of magnetic field lines for current carrying conductor?

Answer 11

Right Hand grip rule
- If thumb is current, fingers is direction of magnetic field
- if fingers is current, thumb is direction of magnetic field

Question 12

What is the equation for magnetic flux density around straight conductor?

Answer 12

B = μI/2πd
μ = permittivity of free space
d = perpendicular distance from point to straight conductor (basically shortest distance)

Question 13

What direction does a compass needle point in?

Answer 13

Direction of net magnetic field

Question 14

What is the earth’s magnetic field caused by?

Answer 14

Electric currents circulating within the core of the earth

Question 15

Where is magnetic south pole of the earth?

Answer 15

At geographical north

Question 16

Where is the magnetic north pole of the earth?

Answer 16

At geographical south

Question 17

How does magnetic field lines travel for earth?

Answer 17

From magnetic north to magnetic south, from geographical south to geographical north

Question 18

What is the magnitude of the magnetic flux density at the centre of circular coil?

Answer 18

B =μNI / 2r
N = number of turns of the coil

Question 19

What does a solenoid consist of?

Answer 19

Many flat circular coils stacked together side by side

Question 20

What is the magnitude of the magnetic flux density inside a solenoid?

Answer 20

B = μnI
n = N / L (number of turns per unit length)

Question 21

What does the insertion of ferromagnetic material change?

Answer 21

It changes the permeability of free space μ0 to permeability of the material μ (where μ > μ0)

Question 22

What is the effect on the magnetic flux density of a current carrying solenoid when a ferrous core is inserted into it?

Answer 22

The magnetic field generated by the current in the solenoid aligns the domains of magnetic dipoles in the ferrous core. The magnetic dipole produce their own magnetic field lines, thus strengthening the existing magnetic flux density by a few thousand times and a much larger magnetic flux density will be created

Question 23

What is magnetic flux density?

Answer 23

Magnetic flux density is the force per unit current per unit length acting on an infinitely long current-carrying conductor placed perpendicular to the magnetic field

Question 24

What is one tesla?

Answer 24

One tesla is the force per unit length of one newton per metre acting on a straight conductor carrying one ampre of current placed normal to the magnetic field

Question 25

What does a mass spectrometer consist of?

Answer 25

Both velocity selector and deflection chamber

Question 26

Is magnetic flux density scalar or vector?

Answer 26

Vector

Question 27

What is the work done of an electron passing through a magnetic field?

Answer 27

There is no work done because W=Fd, where force is in the direction of distance. Since magnetic force is always perpendicular to direction of velocity (direction of electron), therefore work done = 0. Change in kinetic energy is also 0.