electromagnetic induction

Question 1

factors that affect the size and direction of an induced potential difference

Answer 1

1. number of coils of wire
2. speed of rotation
3. magnetic field strength

Question 2

describe how the magnetic field produced, opposes the original change

Answer 2

• the induced current creates a magnetic field around itself where this magnetic field opposes the original change
• ex if a magnetic is moved into a coil of wire the induced magnetic field repels the magnet back out of the coil

Question 2

explain how an alternating current in one circuit can induce a current in another circuit in a transformer
-( what produces alternating magnetic field)
-(what is magnetised and demagnitised)
-(why does the magnetism in the core also alternate)
-(what does this induce in the secondary coil)

Answer 2

• when an alternating potential difference is applied across the primary coil it produces an alternating magnetic field
• the iron in the core is a magnetic material that is easily magnetised and demagnetised
• because the coil is producing an alternative magnetic field the magnetisation in the core also alternates
• this changing magnetic field induces a potential difference in the secondary coil

Question 3

a transformer can change …

Answer 3

the size of an alternating voltage

Question 4

Explain why, in the national grid, electrical energy is transferred
at high voltages from power stations,
and then transferred at
lower voltages in each locality for domestic uses as it improves
the efficiency by reducing heat loss in transmission lines

Answer 4

• needs to transfer loads of energy
  -> so trasnmits energy at a high power
  -» to do this you need a high pd or a high current
• high current makes wires heat up = energy wasted to thermal energy stores
• at towns voltage (and so current) is decreased as higher voltages are dangerous
  -> safe to use
  -> less energy is lost as it carries from power stations
• low voltages are more efficient as higher current = more energy wasted

Question 5

why in the national grid is electrical energy then transferred at lower voltages in each locality for domestic use

Answer 5

• high voltage = danger
• so step down transformers bring it back down to safe usable levels
• as well as making sure less energy is lost as it is carried from power stations
  -> reduces heat loss in transmission lines

Question 6

explain why step-up transformers are used in the transmission of electricity in the national grid

Answer 6

• boost the potential difference really high
• but keep the current low

Question 7

explain why step-down transformers are used in the transmission of electricity in the national grid

Answer 7

• bring the potential difference down to safe and usable levels

Question 8

what is the equation for power for transformers with 100% efficiency

Answer 8

potential difference across primary coil (v) * current in primary coil (A) = potential difference across the secondary coil (v) * current in secondary coil (A)
Vp * Ip = Vs * Is