P7 - Electromagnetic Effects

Question 1

What is produced around a current carrying wire? [1]

Answer 1

A magnetic field

Question 2

How can you determine the direction of a magnetic field around a wire? [1]

Answer 2

Using the Right Hand Grip Rule - Thumb is the direction of current, the field lines wrap around in the direction of your fingers

Question 3

What is a solenoid? [1]

Answer 3

A coil of wire with a magnetic field, which can be used as an electromagnet

Question 4

How can you increase the strength of a solenoid magnet? [3]

Answer 4

Using an iron core / Increasing the number of turns in the coil / Increasing the current

Question 5

What is the motor effect? [1]

Answer 5

When a current carrying wire is placed in a magnetic field it experiences a force, pusing the wire out/away from the field

Question 6

How can you predict the direction of the motor effect? [3]

Answer 6

Flemings Left Hand Rule / Thumb = Movement, First finger = Field, Second finger = Current

Question 7

What kind of current is used in Fleming’s Left Hand Rule? [1]

Answer 7

Conventional current (positive to negative)

Question 8

What factors affect the strength of the electromotive force (e.m.f)? [3]

Answer 8

The length of wire placed in the field / the current in the wire / the strength of the permanent field

Question 9

What are 4 main parts of a motor? [4]

Answer 9

Magnets / coil of wire / power supply / split ring commutator

Question 10

What is the role of the split ring commutator in a motor? [1]

Answer 10

Reverses the current every half turn

Question 11

What is electromagnetic induction? [1]

Answer 11

The production of a potential difference caused by relative movement between a conductor and a magnetic field

Question 12

Describe how an electrical generator works [4]

Answer 12

A turbine spins the coil of wire between the magnets / the wire cuts through the magnetic field experiencing a changing magnetic field / a potential difference is induced / a current is produced

Question 13

What is the difference between direct current (D.C) and alternating current (A.C)? [2]

Answer 13

Direct current only flows in one direction / Alternating current flows in both directions

Question 14

Compare a motor, AC generator and DC generator in terms of a power supply and slit ring commutator [2]

Answer 14

Motor has a power supply but generators do not / motor and DC generator has a split ring commutator but an AC generator has slip rings

Question 15

What is the role of the split ring commutator in a DC generator? [1]

Answer 15

Ensures the current only flows in one direction

Question 16

What is the role of the slip rings in an AC generator? [1]

Answer 16

Ensures current can flow in both directions

Question 17

Describe how transformers work [2]

Answer 17

An alternating current flows through the primary coil, producing an alternating magnetic field / this causes the secondary coil to experience a changing magnetic field, inducing a potential difference which produces an alternating current in the secondary coil

Question 18

Why do step up transformers increase voltage? [1]

Answer 18

There are more coils in the secondary coil so a larger potential difference is induced

Question 19

What is the core made of in a transformer? [1]

Answer 19

Soft iron core

Question 20

Recall the equation that relates the voltage and number of coils in the primary and secondary coils in a transformer [1]

Answer 20

(Vₚ/Vₛ) = (Nₚ/Nₛ)

Question 21

State one assumption used in transformer calculations [1]

Answer 21

The transformer is 100% efficient (the power is assumed to be the same in both coils)

Question 22

Explain why a step up transformer is useful in the transmission of high voltage electricity [3]

Answer 22

P=IV - Power lines have to transmit huge amounts of power - to achieve this you would want a high voltage and high current / High current produces a lot of wasted heat energy due to resistance / We compensate for this by using an extremely high voltage (400,000V)

Question 23

Recall the equation that relates current and voltage in the primary and secondary coils in a transformer [1]

Answer 23

(Iₚ/Vₚ) = (Iₛ/Vₛ)