Electromagnetism

Question 1

Define the Motor effect

Answer 1

When a current carrying wire is placed in a magnetic field at a non-zero angle to the magnetic field lines, it experiences a force due to the field.

Question 2

Define Magnetic flux density

Answer 2

The force per unit length per unit current on a current-carrying conductor at right angles to the magnetic field lines.

Question 3

What is the unit of magnetic flux density?

Answer 3

Tesla

Question 4

what happens to an electron moving in an magnetic field?

Answer 4

It experiences a force due to

Question 5

For the path of a charged particle in magnetic fields which direction does the force act?

Answer 5

At right angles to the velocity

Question 6

What is the motion of a charged particle in a magnetic field?

Answer 6

circular motion

Question 7

What is the work done on a charged particle moving in a magnetic field?

Answer 7

As the charged particles move at right angles to the magnetic field no work is done

Question 8

What is a hall probe and how does it work?

Answer 8

A hall probe is a device used to measure magnetic flux density. It consists of a semiconducting material which is placed perpendicular to a magnetic field and a constant current is passed through it.

Question 9

For a constant current, what is the hall voltage proportional to?

Answer 9

The magnetic flux density

Question 10

What two equations do you equate to find the radius of the particles path?

Answer 10

BQv and (mv^2)/r

Question 11

What is a cyclotron?

Answer 11

A particle accelerator that produces high-energy beams for radiation therapy

Question 12

How does a cyclotron work?

Answer 12

Charged particles are directed into on of the Dees at the Centre of the cyclotron, it is attracted to the negative Dee and the magnetic field causes it to follow a circular path. as it leaves the Dee the voltage reverses and the particles are accelerated to the other Dee. This causes the kinetic energy of the particles to increase and therefore the radius of their path also increases. These particles spiral outwards gaining speed until the reach the place where the beam is emitted

Question 13

What is a mass spectrometer?

Answer 13

It is used to analyse the type of atoms present in a sample.

Question 14

How does a mass spectrometer work?

Answer 14

The atoms of a sample are ionized and directed in a narrow beam at the same velocity in a uniform magnetic field. The ions are deflected in a semicircle by the magnetic field onto a detector. The radius of the path of each ion depends on its specific charge therefore each type of ion reaches a different position on the detector so the detector then determines the abundance of each ion.

Question 15

What is a velocity selector?

Answer 15

A component that ions pass through in order to have the same velocity as they enter the magnetic field

Question 16

What is electromagnetic induction?

Answer 16

When a wire and a magnetic field are moved relative to one another a small potential difference is induced between the ends of the wire

Question 17

Why is an electric current induced when a current carrying wire is in a magnetic field?

Answer 17

This occurs because the free electrons in the wire experience a force towards one end of the wire

Question 18

How can induced emf be increased?

Answer 18

1.By moving the wire faster
2.Using a stronger magnet
3.Making the wire into a coil and moving the magnet in and out

Question 19

Is an emf induced when the wire if parallel to the magnetic field lines?

Answer 19

No because for an emf to be induced, the wire must cut lines of the magnetic field

Question 20

How does a dynamo work?

Answer 20

The magnet in the dynamo spins and an emf is induced in the coil

Question 21

What is the dynamo rule?

Answer 21

flemings right hand rule

Thumb-motion
Pointer- field
Middle - current

Question 22

In a solenoid, if the current passes anti clockwise which pole is it?

Answer 22

North

Question 23

In a solenoid, if the current passes clockwise which pole is it?

Answer 23

South

Question 24

How does a magnet in a coil obey conservation of energy?

Answer 24

It will act against the incoming pole so as a North Pole is brought towers a coil the end closest to the magnet must become a north pole and when its pulled away again the end closest to the North Pole becomes a South Pole to resist the motion.

Question 25

What is Lenz’s law?

Answer 25

The direction of the induced current is always such as to oppose the change that causes the current

Question 26

Define magnetic flux

Answer 26

The magnetic flux density per unit area passing at right angles through the area

Question 27

What is the unit of magnetic flux?

Answer 27

The weber

Question 28

Define emf in terms of magnetic flux

Answer 28

EMF is the magnetic flux swept out by the conductor each second

Question 29

What happens when you turn the coil through 180*?

Answer 29

Flux linkage becomes -BAN

Question 30

What happens to the flux linkage when the magnetic field is parallel to the coil area?

Answer 30

The flux linkage is 0 as no field lines pass through the coil area

Question 31

What is Faradays law of electromagnetic induction?

Answer 31

The induced emf in a circuit is equal to the rate of change of flux linkage through the circuit