# Electromagnetism Flashcards

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1
Q

Define magnetic flux.

A

The product of magnetic flux density perpendicular to the area and the area.

2
Q

Define the weber.

A

A change in flux of one weber per second will induce an emf of 1V in a loop of wire. This is one tesla meter-squared.

3
Q

A

The product of magnetic flux and the number of turns in the coil.

4
Q

A

The magnitude of the induced emf is equal to the rate of change of magnetix flux linkage.

5
Q

When do we use the equation for magnetic flux?

A

When the magnetic flux density is not perpendicular to area. cos(x) is used, where x is the angle between the direction of the magnetic field and the normal to the coil.

6
Q

State Lenz’s law.

A

Any induced current or induced emf will be established in a direction so as to produce effects which oppose the change that is producing it.

7
Q

How do we calculate induced emf?

A

Change in magnetic flux linkage over change in time.

8
Q

Describe the function of a simple AC generator. Explain how this works.

A

To convert kinetic energy into chemical energy by inducing an electric current by rotating a coil in a magnetic field. The output voltage and current change with every half turn of the coil.

9
Q

When do we obtain an induced emf and induced current?

A

When the lines of flux are cut by a conductor of electricity. A current will only be induced if the conductor is connected to a complete circuit.

10
Q

Describe the function of a simple transformer.

A

To change the voltage of an alternating current.

11
Q

What is the turns-ratio equation and when do we use it?

A

The ratio of primary voltage over secondary voltage is equal to the ratio of primary turns over secondary turns. This allows us to calculate the input or output voltage, providing we know the number of turns in both the primary and secondary coils.

12
Q

Describe the functions of step-down and step-up transformers.

A

Step-down transformers reduce the voltage by having fewer turns on the secondary coil than the primary.
Step-up transformers increase the voltage by having more turns on the secondary coil than the primary.

13
Q

What is a transformer made of?

A

Two coils of wire wrapped around an iron core.

14
Q

Explain how a transformer works.

A

The alternating current in the primary coil induces a magnetic field which is then passed around the iron core to the secondary coil. This induces an emf in the secondary coil.

15
Q

Describe how transformers are used in the national grid.

A

Electricity is sent out from power stations with the lowest possible current to reduce losses due to the resistance in the cables. To achieve this we use a step-up transformer to achieve a voltage of around 400000V to transmit the power, and step down transformers to reduce the voltage to about 230V for domestic use.