Magnetic Fields

Question 1

What is a Magnetic field?

Answer 1

a region where a force is exerted on a magnetic material

Question 2

What is the direction of the magnetic field?

Answer 2

North to South

Question 3

What are the field lines on a current carrying wire?

Answer 3

the field lines are concentric circles centred around the wire

Question 4

How can we find the direction of the magnetic field for a current carrying wire?

Answer 4

right hand rule

Question 5

What is a solenoid?

Answer 5

consists of a wire coiled up into a spiral shape

Question 6

What happens when you place a current carrying wire in a magnetic field?

Answer 6

the field around the wire and the field from the magnets interact. the field lines from the magnet contract to form a “stretched catapult” effect where the flux lines are closer together. i.e causes a force on the wire

Question 7

what happens if the current is parallel to the magnetic field lines?
- what condition must be kept?

Answer 7

no force acts
- the current has to be perpendicular

Question 8

How do you find the direction of the force?
- what does each finger represent?

Answer 8

• Flemings Left Hand rule
• thumb: force
  first finger: magnetic field
  middle finger: current

Question 9

What is the equation for the Force on a current-carrying wire in a magnetic field?

Answer 9

F= BIL

Question 10

What is the magnetic flux density?
Units?

Answer 10

• the force per unit length per unit current on a current carrying conductor at right angles to the magnetic field lines.
• Tesla, T

Question 11

what is magnetic flux density a measure of?

Answer 11

the number of field lines passing through the region of space per unit cross-sectional area

Question 12

What is the equation for the Force on charged particles moving in a magnetic field?

Answer 12

F= Bqv

Question 13

How are charged particles deflected in a magnetic field?

Answer 13

charged particles are deflected in a circular path

Question 14

what is an application for the circular deflection of charges particles in a magnetic field?

Answer 14

a cyclotron, used for radiotherapy

Question 15

What is the function of a cyclotron?

Answer 15

uses a magnetic field to keep charged particles moving in a circle and electric field to accelerate
-produces X-rays

Question 16

what is the equation for the radius of curvature of a charged particle?

Answer 16

r= mv/BQ

Question 17

How does a cyclotron work?

Answer 17

charged particles move in a circle due to the magnetic field , and the two Dees are electric plates which cause the charged particles to increase in speed between the plates. this increases r and the polarity of the plates is reversed to produce spiral motion.

Question 18

what is the equation for the time of a particle in an orbit in a cyclotron?

Answer 18

t= 2πm/BQ

Question 19

what is a velocity selector?

Answer 19

a device that uses perpendicular electric and magnetic fields to select charged particles with a specific velocity

Question 20

What feature does the ion need to go through a velocity selector?

Answer 20

equal top charge

Question 21

What is Faraday’s law?

Answer 21

when the magnetic flux linkage in a circuit changes, an electromotive force is induced in the circuit

Question 22

what is the equation for Faraday’s law?

Answer 22

emf= -N Δφ/Δt

Question 23

What is Lenz’s law?

Answer 23

the inducted electromotive force will induce a current and a magnetic field which will oppose the change in flux

Question 24

what is magnetic flux linkage?

Answer 24

the product of the magnetic flux and the number of turns on a coil through which the field passes

Question 25

what is the equation for magnetic flux?

Answer 25

φ= BAcosθ

Question 26

what is the equation for magnetic flux linkage?

Answer 26

Nφ= BANcosθ