Electromagnetic Induction & Alternating Current

Question 1

Electromagnetic induction

Answer 1

The εmf produced across a conductor exposed to a varying magnetic field

Question 2

Fleming’s right hand rule

Answer 2

Predicts the direction that an induced current flows, e.g. when a wire is moved through the magnetic field between two magnets

Question 3

Fleming’s left hand rule

Answer 3

Predicts the the direction of the force on a current-carrying conductor in a magnetic field, e.g. it predicts the direction of rotation of an electric motor

Question 4

What conclusions did Faraday come to when experimenting with magnetic fields and electromagnetic induction?

Answer 4

• when a conductor is moved through a magnetic field, the magnitude of the induced εmf is equal to the rate at which magnetic flux is cut through by the conductor
• when a magnet is moved near a coil, the magnitude of the induced εmf is equal to the rate of change of flux multiplied by number of turns in the coil, the rate of change of flux linkage

Question 5

Faraday’ law

Answer 5

When the magnetic flux linking a circuit changed, and εmf is induced in the circuit proportional to the rate of change of the flux linkage. The equation linking εmf, E, to flux linkage is
E = NΔΦ/Δt

Question 6

Lenz’s law

Answer 6

The direction of an induced current opposes the change of magnetic flux that produces it

Question 7

Eddy currents

Answer 7

Finish

Question 8

When a current is induced due to a change in magnetic field, where does the energy to drive this current come from?

Answer 8

It comes from the work done in moving the conductor or magnetic field against the repulsive force created from the induced current. Lenz’s law

Question 9

Generator

Answer 9

In the context of electromagnetic induction: It consists of a rotating coil within a magnetic field and is used to generate an alternating current by electromagnetic induction

Question 10

Peak voltage

Answer 10

The maximum value for an alternating εmf and so is the highest amplitude value of the εmf

Question 11

Peak-to-peak voltage

Answer 11

The difference between the maximum and minimum values for an alternating εmf, twice the amplitude of the εmf

Question 12

What does the equation

ε = BAN ωsinωt describe?

Answer 12

How the εmf induced in a coil rotating uniformly in a uniform magnetic field varies with time

Question 13

Root mean square (rms)

Answer 13

The value of an ac current or potential difference that is equal to the dc value that would lead to the same power being dissipated in a resistor

Question 14

The average power dissipated in a resistor by an ac current is

Answer 14

P(av) = I²(rms)R = V(rms)I(rms)

Question 15

The resistance in a circuit produced by an ac current is

Answer 15

R = V(rms)/I(rms) = Vo/Io

Question 16

Oscilloscope

Answer 16

A cathode ray oscilloscope is used for measuring dc and ac voltage, measuring time intervals and frequencies and also displaying alternating waveforms

Question 17

Time base

Answer 17

The control on an oscilloscope that determines the speed at which the electron beam moves horizontally across the screen

Question 18

How can you measure the ac frequency from an oscilloscope when it’s input control is set to AC, and a signal generator is set to its some function and connect to the y-input?

Answer 18

Time period = number of divisions for one cycle x time base setting

Question 19

How can you calculate the εmf of a battery connected to an oscilloscope set to DC?

Answer 19

ε = number of divisions (where line rests) x y-gain (number of V/div)

Question 20

An oscilloscope screen is an

Answer 20

Adjustable voltage versus time graph

Question 21

The sensitivity of the vertical axis on an oscilloscope screen can be adjusted using

Answer 21

the y-gain control

Question 22

The sensitivity of the horizontal axis on an oscilloscope screen can be adjusted using

Answer 22

the time base control