Chapter 23 Magnetic Fields Flashcards
How are magnetic field lines drawn?
- 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
When a wire carries current…
…A magnetic field is produced
What happens when a charged particle moves?
It creates a magnetic field
What is the right hand grip rule? What does it show?
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.
What is the strength of a magnetic field measured in?
Tesla
units T
What is flemings left hand rule and what does it show?
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
What is thumb on flemings left hand rule?
Motion, direction of the force
What is the second finger for flemings left hand rule?
Direction of the current
What is the first finger for flemings left hand rule?
Magnetic field direction
What is the equation to find the magnitude of the force on a wire placed in a magnetic field?
F = BILSinθ F = Force B = Magnetic flux density (tesla) L = Length of wire in field Sinθ = Angle between magnetic field and current direction
What is the equation for the force on a wire when it is 90* to the magnetic field?
B = F / IL
How is the magnetic flux density calculated in a lab?
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
What happens to electrons passing through a magnetic field?
they follow the magnetic field lines
What is the equation for charged particles through a magnetic field?
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
What is the path for an electron passing through a uniform magnetic field? Why?
It is circular path because the force is always perpendicular to the direction of travel
What is the equation for a particle passing through a uniform field?
r = mv / BQ r = radius m = mass v = velocity B = Magnetic Flux density Q = Charge
How is the equation for a particle passing through a uniform field derrived?
F = mv^2 / r (Centripetal force equation) F = BQv BQv = mv^2 / r BQ = mv / r r = mv / BQ
What does the equation r = mv / BQ show us?
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
What is a velocity selector?
It is a device that uses electric and magnetic fields to select charged particles of a specific velocity.
What does a velocity selector consist of?
It consists of a magnetic field perpendicular to an electric field.
How does a velocity selector work?
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.
