Transformers, microphones, speakers and electromagnetism

Question 1

What are:

Induced magnets

Answer 1

Magnets that become magnetic in the presence of a magnetic field

Question 2

What are the main:

Magnetic materials

Answer 2

Iron, steel(iron alloy), nickel, cobalt (neodymium)

Question 3

What is a:

Magnetic field

Answer 3

The region around a magnet where a force acts on another magnet or magnetic material

force for north magnet

Question 4

What is a:

Solenoid

Answer 4

a coil of wire in turns which focuses the magnetic field

Question 5

How to increase the:

strength of a solenoid’s magnetic field

Answer 5

• Add an iron core
• Increase the number of coils
• Increase the current
• Increase the strength of the magnet by using a stronger material

Question 6

What affects the:

Force on a conductor

formula

Answer 6

• Magnetic flux density
• Current
• Length
• F = Bi l

Question 7

What is the:

Generator effect

Answer 7

1. A change in magnetic field arounld a conductor
2. Potetntial difference is induced (across the ends of the conductor)
3. If there is a circuit, current is induced
4. An induced current generates a magnetic field that opposes the original change, movement of conductor or change in magnetic field

Question 8

How to:

Increase the generator effect

Answer 8

• Coil of wires rotated faster
• Magnetic field strength is increased
• number of turns on wire of coil is increased

Question 9

How to:

Change the direction of current in a dynamo

Answer 9

• Swapping the polarity of both magnets
• Reversing the direction of roation of the coil, reversing the direction of the induced potential difference

Question 10

What is the difference between:

Alternators and dynamos

Answer 10

Alternators has 2 commutators which stay on the same wire, leading to current changing direction. Dynamos have 1 split ring commutator so the current goes the same direction at all times

Question 11

How is:

Voltage calculated in a dynamo

Answer 11

As a mean of the voltage, which resembles a sin graph

Question 12

How to change:

Alternating current into direct

Answer 12

Use a diode

Question 13

When is the:

Output of a generator greatest

Answer 13

• When the magnetic field lines are being broken at the fastest rate
• This is when the coil is moving vertically upwards, when the wire and magnetic field is horizontal
• No current induced when coil moves parallel to magnetic field lines

Question 14

What are:

Microphones

Answer 14

• Devices that use the generator effect to convert pressure variation in sound waves into variations in current in eletrical circuit
• When diaphragm is hit, the coil of wire moves relative to the magnet leading to generator effect
• Loudspeakers are the opposite, and use the motor effect to cause pressure variations

Question 15

What does a:

Basic transformer consist of

Answer 15

• Primary coil
• secondary coil
• iron core as it easily magnetized and de-magnetized

Question 16

What are the:

2 types of transformers

Answer 16

• Step up - voltage increases
• Step down - voltage decreases but current increases

Question 17

What is the:

formula for voltage across transformers

Answer 17

Vp/Vs = Np/Ns where N is number of turns

Question 18

What would be the case if:

Transformers were 100% efficient

Answer 18

• electrical power input would = electrical power output
• Vs * Is = Vp * Ip

Question 19

How do:

Transformers work

Answer 19

• AC flowing through primary coil
• Produces an alternating magnetic field in the iron core
• Secondary side has a coil of wire with alternating magnetic field
• Magnetic field moves
• induces a potential different, generator effect

Question 20

Uses of:

Transformers

Answer 20

• More effective transmission of electricity in national grid
• Produced at 15,000V, step up to 400,000, step down to 230
• This is as increasing voltage decreases current, as current and pd are inversely proportional
• Leads to powerlines heating up less and less energy lost as heat

Question 21

Do different wires

Answer 21

Earth, live, afdsf