Chapter 23 Magnetic Fields

Question 1

How are magnetic field lines drawn?

Answer 1

• Arrow of the magnetic fields shows the direction in which the force acts
• Equally spaced lines indicate a uniform field
• The field is stronger when the lines are closer together
• Like polls repel

Question 2

When a wire carries current…

Answer 2

…A magnetic field is produced

Question 3

What happens when a charged particle moves?

Answer 3

It creates a magnetic field

Question 4

What is the right hand grip rule? What does it show?

Answer 4

It shows where the direction of the magnetic field based off a current flowing through a wire.
Make your right hand into a thumbs up shape.
The direction of your thumb is the direction of the current through a wire.
The direction of the rest of your fingers shows where the magnetic field lines are.

Question 5

What is the strength of a magnetic field measured in?

Answer 5

Tesla

units T

Question 6

What is flemings left hand rule and what does it show?

Answer 6

It shows the force applied to a wire with current flowing through it when it is placed in a magnetic field.
- ThuMb indicates motion, the direction of the force
- First finger is for Field, the direction of the field
- SeCond finger is for the direction of the current flowing through a wire
If you have 2 of the 3 parts you can find the other one

Question 7

What is thumb on flemings left hand rule?

Answer 7

Motion, direction of the force

Question 8

What is the second finger for flemings left hand rule?

Answer 8

Direction of the current

Question 9

What is the first finger for flemings left hand rule?

Answer 9

Magnetic field direction

Question 10

What is the equation to find the magnitude of the force on a wire placed in a magnetic field?

Answer 10

F = BILSinθ
F = Force
B = Magnetic flux density (tesla)
L = Length of wire in field
Sinθ = Angle between magnetic field and current direction

Question 11

What is the equation for the force on a wire when it is 90* to the magnetic field?

Answer 11

B = F / IL

Question 12

How is the magnetic flux density calculated in a lab?

Answer 12

A horse shoe magnet is placed side ways on a balance. A wire with a know current is placed between the magnet. The amount of wire in the magnet is then measured. Then the force on the balance is read and the equation: B = F/IL is used

Question 13

What happens to electrons passing through a magnetic field?

Answer 13

they follow the magnetic field lines

Question 14

What is the equation for charged particles through a magnetic field?

Answer 14

F = BeV
F = Force
B = The magnetic flux density 
e = Charge on an electron or protons (or the charge for a particle)
v = Velocity of the particle

Question 15

What is the path for an electron passing through a uniform magnetic field? Why?

Answer 15

It is circular path because the force is always perpendicular to the direction of travel

Question 16

What is the equation for a particle passing through a uniform field?

Answer 16

r = mv / BQ
r = radius
m = mass
v = velocity
B = Magnetic Flux density
Q = Charge

Question 17

How is the equation for a particle passing through a uniform field derrived?

Answer 17

F = mv^2 / r (Centripetal force equation)
F = BQv 
BQv = mv^2 / r 
BQ = mv / r
r = mv / BQ

Question 18

What does the equation r = mv / BQ show us?

Answer 18

It shows us that the radius is proportional to speed and mass. r ∝ v
So a larger particle moves in larger circles. r ∝ m
Stronger magnetic fields make particles move in smaller circles. r ∝ 1/B
Particles with greater charges move in smaller circles.
r ∝ 1 / Q

Question 19

What is a velocity selector?

Answer 19

It is a device that uses electric and magnetic fields to select charged particles of a specific velocity.

Question 20

What does a velocity selector consist of?

Answer 20

It consists of a magnetic field perpendicular to an electric field.

Question 21

How does a velocity selector work?

Answer 21

Charges are deflected by the magnetic and electric fields and only charges of a specific speed will these deflections cancel out and travel in a straight line emerging from the velocity selector.