Magnetic fields (unit 4)

Question 1

Number of times proton moves between a gap in a cyclotron?

Answer 1

ev divided by pd

Question 2

How to work out where the force acts ON the wire?

Answer 2

-Fleming’s left hand rule

Question 3

How to work out force acting on the current carrying wire?

Answer 3

-BIL sin theta

Question 4

How to work out force for individually charged particles?

Answer 4

-BQV sin theta

Question 5

Unit for magnetic field?

Answer 5

-Tesla (T)

Question 6

How does Hall Voltage work?

Answer 6

-When a current flows at 90° through a magnetic field, there
will be a force on the electrons
-forcing them to one surface of the conductor.
-causing one surface to become negative and the other positive.
This creates an electrical field between the surfaces and cause
a force on the electrons in the opposite direction.
-the magnetic force and the electrical force will balance and an equilibrium is
reached.
-Hall voltage is the pd between surfaces at this equilibrium

Question 7

How to work out Hall Voltage?

Answer 7

Hall Voltage =Bvd

Question 8

What does the magnetic field look like in a straight wire?

Answer 8

• circles going around wire ( use right hand grip rule to determine direction of field)

Question 9

What does the magnetic field look like in a solenoid?

Answer 9

• looks like a bar magnet (direction is the same as direction of current)

Question 10

How to work out B in a wire?

Answer 10

• B = π µ 0 I/ 2 pi a

a is the distance from wire (radius for where you want field)

Question 11

How to work out B in a solenoid?

Answer 11

-B = μo nI

n is number of turns per meter
n= number of turns/ length

Question 12

How to increase field strength in a solenoid?

Answer 12

-adding an iron core

Question 13

How do parallel current carrying wires exert a force on eachother?

Answer 13

• When a current passes through a wire it creates a magnetic field.
  -the top wire will have a magnetic FIELD towards the bottom one (right hand grip rule)
  -As current perpendicular to this field, due to LHR bottom wire there is a force on top wire from bottom
  -due to Newton’s third law , there will be an equal force emitted by both wires on each other

Question 14

What happens when putting a charged particle in a uniform magnetic field?

Answer 14

-Magnetic forces always act perpendicular to the motion. Therefore,
the magnetic force acts as a centripetal force and makes the charges
move in a circular path.

Question 15

How to work out B field in uniform magnetic field?

Answer 15

BQV= mv^2/r

Question 16

What happens when putting a charged particle in a uniform electric field?

Answer 16

-The electrical force between two parallel plates is constant due to the uniform electric field.
- the force acting on the electron here, will cause a vertical acceleration but not
change its horizontal velocity.

Question 17

How do particle accelerators work?

Answer 17

-when the force and motion are in the same direction, the particle will gain kinetic energy as it is accelerated by the electric field
- use an alternating p.d. to accelerate the particles in the gaps between electrodes.

Question 18

How to work out increase in KE in a particle accelerator?

Answer 18

-q x PD

Question 19

How to work out acceleration in uniform electric field?

Answer 19

• F=ma
  -qv/d = ma

Question 20

Linear particle accelerator?

Answer 20

• path - straight line
• magnetic field - none
  -alternating PD - Constant, increasing length of tube ensuresthe p.d. changes in time

Question 21

Cyclotron particle accelerator?

Answer 21

• path - Circular but with increasing radius
  -magnetic field - Constant, to ensure circular motion
  -alternating PD - Constant, increasing path length ensures the p.d. changes
  in time

Question 22

Synchotron particle accelerator?

Answer 22

-path - Circular, constant radius
-magnetic field - Increasing to ensure circular motion with constant r
-alternating PD - Increasing

Question 23

How to work out frequency for a CYCLOTRON and SYNCHOTRON?

Answer 23

F = BQ/2piM
​

Question 24

How to derive equation for frequency for CYCLOTRON and SYNCHOTRON?

Answer 24

BQV= mv^2/r
v=ωr and ω=2πf

Question 25

What direction does conventional current flow?

Answer 25

-opposite flow of electrons

Question 26

INVESTIGATION OF MAGNETIC FLUX DENSITY USING A HALL PROBE practical ?

Answer 26

-Place the Hall probe into a known magnetic field, B1 and note the Hall potential difference, V1 -Then place the Hall probe in the centre of a solenoid -Ensure, in both cases, the probe is at 90o to the magnetic field - Again measure the Hall potential difference, V2 when the probe is in the solenoid The unknown magnetic field of the solenoid, B2, can be found using 𝐵2 =(B1 V1) /V2