Magnetism and Magnetic Materials
Electromagnetism
Motor Effect / DC Motors and Loudspeakers
Electromagnetic Induction / Generators
Transformers
100
List 4 magnetic materials
Iron, steel, nickel and cobalt
100
A wire has a current directed into the board. Draw the magnetic field around the wire.
Clock-wise circle
100
What are two things you could do to increase the strenth of the motor force acting on a wire?
Incrase the current in the wire
Increase the strength of the permanent magnets
100
A generator converts _________ energy into _________ energy.
Mechanical (kinetic)
Electrical
100
1. What is the difference between a step-up and step-down transformer?
2. If a transformer has 100 loops in its primary coild and 700 loops in the secondary coil is it a step-up or step-down transformer?
1. Step-up increases voltage
Step-down decreases voltage
2. Step-up transformer
200
What direction to magetic field lines point?
N -> S
200
What are the different parts of an electromagnet?
Solenoid and soft core
200
How would switching the terminals of a battery connected to a DC motor effect the motor?
Since the current would flow in the opposite direction the motor would spin in the opposite direction.
200
What is a dynamo? Where do you see it used?
A small generator that produces DC current
Used in bicycles to power lights
200
Where are step-up and step-down transformers used in the national grid?
Step-up: increases the voltage leaving the power plant and going to the transmission lines
Step-down: decreases the voltage from the transmission lines as it reaches the consumer
300
What do we call a magnetic material that can be easily magnetized, but quickly loses its magnetism?
Provide an example of one.
Soft magnetic material
Iron
300
What are three ways you can increase the strength of an electromagnet?
Increase the current
Increase the number of turns
Add an iron core
Pack the coils together more tightly
300
What direction will the motor force acting on this current carrying wire be in?
Downward
300
What are three factors that effect the strength of the induced voltage in a generator?
Speed at which the coductor / magnet moves
Strength of the magnetic field
Number of loops in the coil
300
What is the purpose of increasing the voltage of the elctricity in the transmission lines?
Current and voltage are inversely proportional (when power is constant P=IV). So, increasing the current decreases the current which results in less energy loss (less current = less heat produced in the wires)
400
Where is the magnetic field around a permanent magnet strongest?
How can you tell the strength of a magnetic field from a field diagram?
At the poles
How close together the field lines are
400
Describe one real-world applcation of electromagnets.
Relay switch, circuit breaker, scrapyard crane, electric bell / buzzer, etc.
400
What is the purpose of a split ring commutator in an electric DC motor?
It reverses the current every half turn to ensure the force acts in the same direction on each side of the motor so it continuously rotates in one direction.
400
When a magnet is pushed into a coil of wire it causes a current to flow from left to right. What happens to the current whent he magnet is pulled out of the coil?
The current flows in the opposite direction - from right to left
400
Assume the efficieny of this transformer is 100%. Calculate the ouput current in the secondary coil.
P1 = P2
I1V1 = I2V2
I2 = I1V1 / V2
I2 = 10(250) / 1000
I2 = 2.5A
500
Draw the magnetic field lines around a permanent bar magnet.
500
Which side of this electromagnet (the head of the nail or the sharp tip) is the N pole?
The sharp end
Electromagnets have a magnetic field that looks identical to a permanent bar magnet. The side where the current is leaving is the N pole, where the current is enertering is the S pole.
500
Explain how a loudspeaker works?
An alternating current flows through a coil of wire wrapped around a permanent magnet -> as the direciton of the current changes the direction of the magnetic field changes -> causes a change in the direction of the motor firce the wire experiences -> causes the coil of wire to oscillate back and forth -> causes the speaker cone attached tot he coil of wire to vibrate -> vibrations create sound waves
500
Explain how a generator works at a coal powerplant.
Combusting coal releases heat -> heat is used to boil water to make steam -> steam is directed past turbine blades and causes them to spin -> generator is connected to turbine and coil of wire spins in a magnetic field -> voltage is induced and current begins to flow
500
The powerstation generatres electricity at 25,000 V.
A transfomer increases the voltage to 400,000 V before the electricity is transported large distances over the transmission lines.
The number of turns in the secondary coil is 500,000. How many turns are in the primary coil?
n1/n2 = V1/V2
n1 = V1n2 / V2
n1 = 25,000(500,000) / 400,000
n1 = 30,000 turns