Faraday's Law, Lenz's Law and Alternating Currents

Question 1

What is an induced emf?

Answer 1

An induced emf is directly proportional to the rate of change of flux linkage

Question 2

Faraday’s Law

Answer 2

Magnitude of emf = N(change in magnetic flux)/time

Question 3

Induced EMF for conducting rod

Answer 3

BLv

Question 4

Lenz’s Law

Answer 4

The induced emf is always in such a direction as to oppose the change that caused in

Question 5

Equation for Induced EMF in a rotating coil

Answer 5

NBAwsin(wt)

Question 6

Equation for Flux Linkage in a rotating coil

Answer 6

NBAcos(wt)

Question 7

How to find Voltage RMS

Answer 7

Vpeak/sqrt2

Question 8

Current rms

Answer 8

Currentpeak/sqrt2

Question 9

Ohm’s Law

Answer 9

V = IR

Question 10

Equation for Powe

Answer 10

IV

Question 11

Ideal Transformer Equation

Answer 11

Vp/Np = Vs/Ns

Question 12

How to identify a Step-Up Transformer?

Answer 12

Np<Ns then Vp<Vs
Voltage across secondary coil is larger

Question 13

How to identify a Step-Down transformer?

Answer 13

Ns<Np then Vs<Vp
Voltage across secondary coil is smaller

Question 14

What is an ideal transformer

Answer 14

A transformer where there is no energy loss

Question 15

How can energy be lost in a transformer?

Answer 15

Due to heat in the primary and secondary coils
Energy to magnetise the iron core

Question 16

How to prevent energy loss?

Answer 16

Use thick copper wire with less resistance
Use magnetically ‘soft’ material, which means not much energy needed to magnetise or demagnetise core

Question 17

Reducing Eddy Currents

Answer 17

Use laminated cores - made up of strips of iron glued together

Question 18

How to calculate transformer efficiency

Answer 18

Pout/Pin or IsVs/IpVp

Question 19

Equation for Power

Answer 19

E/T