P15

Question 1

4 Examples of devices that use electromagnets?

Answer 1

• Scrapyard cranes
• circuit breaker
• electric bell
• the relay

Question 2

Solenoid rule?

Answer 2

north pole - current anticlockwise

south pole - current clockwise

Question 3

D. Electromagnetic induction?

Answer 3

The process of inducing a potential difference in a wire by moving the wire so it cuts across the lies of a force of a magnetic field

Question 4

D. The generator effect?

Answer 4

The production of a potential difference using a magnetic field

Question 5

The faster a conductor crosses through the lines of a magnetic filed…

Answer 5

… the bigger the induced potential difference is

Question 6

Direction of an induced current always…

Answer 6

opposes the original change that caused it

Question 7

Steo up transformer?

Answer 7

used to increase the size of the potential difference

Question 8

Step down transformer?

Answer 8

used to decrease the size of the potential difference

Question 9

How do transformers work?

Answer 9

• alternating current passing through primary coil generates alternating magnetic field in iron core
• lines of alternating magnetic field in iron core pass through the secondary coil
• magnetic field in secondary coil induces alternating p.d between terminals of the secondary coil

Question 10

Why do transformers work only with AC?

Answer 10

Because changing magnetic field is necessary to induce ac in secondary coil

Question 11

What are the components of a transformer?

Answer 11

iron core. primary coil. secondary coil

Question 12

E. Transformer equation?

Answer 12

primary p.d / secondary p.d = number of primary turns/ no. secondary turn

Question 13

For step down transformer, Ns is…

Answer 13

less then Np

Question 14

100% efficient transformer?

Answer 14

Vp x Ip = Vs x Is

Question 15

Function of low P.D in the grid?

Answer 15

reduces current needed, so reduces power loss and makes system more efficient

Question 16

What is a simple a.c. generator made from?

Answer 16

a coil that spins in a uniform magnetic field

Question 17

Difference between simple d.c generator and a simple a.c generator?

Answer 17

D.c has a split-ring commutator instead of 2 slip rings

Question 18

Waveform on an oscilloscope of an A.C generators induced voltage?

Answer 18

• its peak value when sides of coil cross directly through magnetic field lines
• 0 value when sides of coil move parallel to the magnetic field lines

Question 19

D. Dynamo?

Answer 19

Direct-current generator