P13 | EM induction

Question 1

what is electromagnetic induction?

Answer 1

the induction of a potential difference across a conductor which is experiencing a change in the external magnetic field

Question 2

what type of current does electromagnetic induction produce?

Answer 2

alternating current

Question 3

two ways of inducing a potential difference/current:

Answer 3

• moving a current-carrying wire in a magnetic field

- moving a magnet through a loop/coil of wire

Question 4

four ways of increasing size of induced potential difference/current:

Answer 4

• increase the speed of the magnet being moved
• increase the strength of the magnetic field
• increase the number of loops in the coil of wire
• wrap the coil around a soft iron core

Question 5

what are transformers made from?

Answer 5

two soft iron cores each surrounded by a coil of wire

Question 6

how do transformers work?

Answer 6

by supplying an alternating current to the primary coil of wire, which induced a magnetic field (looks like a solenoid)

Question 7

how does the LHS induce a current on the RHS?

Answer 7

• on the RHS there is an alternating current and a secondary coil of wire
• the alternating magnetic field from the LHS induces an alternating potential difference on the RHS thus producing an alternating current

Question 8

why do power lines have such high voltages?

Answer 8

high potential difference = less current
less current = less heat produced
less heat = less energy wasted

Question 9

why do we use step up transformers?

Answer 9

• transmission wires are long = high resistance
• increasing the resistance cause the wires to heat up
• heat energy is wasted/lost to the surroundings therefore the wires are NOT 100% efficient
• step up transformers increase the p.d. by increasing the number of secondary coils
• increasing the p.d decreases the current which decreases heat loss
• making transmission more efficient

(then we step down the p.d. to make it safer)

Question 10

advantages of power transmission using high voltage cables explained with equations:

Answer 10

• transferring lots of electrical energy per second means there must be high power using P = E ÷ t
• since P = V x I, to transmit electricity at high power there must either be a high current or high potential difference
• the power lost in a wire will be due to the heating effect as electrons collide with the lattice
• this means the energy lost is actually due to the current and the resistance of the wires and can be calculated using P = I^2R
• since Vp x Ip = Vs x Is, we can see that increasing the p.d. of the secondary coil will lower the current in the secondary coil
• increasing the p.d. in the secondary coil can be done using as step up transformer since Ns > Np and
  Vp/Vs = Np/Ns

Question 11

what can transformers change about an alternating voltage?

Answer 11

the size