Chapter 7 Electromagnetic induction

Question 1

What is electromagnetic induction?

Answer 1

The process of generating an EMF (voltage) in a conductor when it experiences a changing magnetic flux.

must be** relative motion **between the conductor and magnetic field

Question 2

State Faraday’s Law of Electromagnetic Induction.

Answer 2

The induced EMF in a coil is equal to the negative rate of change of magnetic flux:
** ε = -N dΦ/dt.**

the negative accounts for Lenz law (direction)

Question 3

What does the negative sign in Faraday’s Law represent?

Answer 3

It shows that the induced EMF opposes the change in flux (Lenz’s Law).

Question 4

State Lenz’s Law.

remember rule for picking direction of current for a solinoid, thumb points to north

Answer 4

The direction of induced current is such that it opposes the change in magnetic flux that produced it.

Question 5

What is magnetic flux?

Answer 5

Φ = B·A·cosθ,
where
B = magnetic field (T),
A = area (m²),
θ = angle between field and normal to surface.

Question 6

How can EMF be increased in induction?

Answer 6

Increase the number of turns, increase the strength of B, increase the area, or increase the rate of flux change.

Question 7

What is a generator?

Answer 7

A device that **converts mechanical energy into electrical energy **using electromagnetic induction.

Question 8

How does an AC generator work?

Answer 8

A coil rotates in a magnetic field, changing flux through the coil and inducing an alternating EMF.

Question 9

What is the difference between AC and DC generators?

Answer 9

AC generators use slip rings to produce alternating voltage; DC generators use a **split-ring commutator **to produce a one-directional current.

Question 10

What is a transformer?

Answer 10

A device that changes the voltage of an AC supply using electromagnetic induction between primary and secondary coils.

Question 11

What is the transformer equation?

Answer 11

Vp/Vs = Np/Ns,
where
V = voltage
N = number of turns on each coil.
P- primary
S- secondary

Remember current is inversely proportional to voltage or Is/Ip

Question 12

What is the power equation for an ideal transformer?

Answer 12

VpIp = VsIs
(input power = output power, ignoring losses).

Power= VI

Question 13

What are sources of transformer energy loss?

Answer 13

Resistance in coils (heat), eddy currents in core, hysteresis in core, flux leakage.

Question 14

How are transformer energy losses reduced?

Answer 14

Use thick copper wires (low resistance), laminated iron core (reduce eddy currents), soft iron core (reduce hysteresis), and tight coil windings (reduce flux leakage).

Question 15

What is back EMF in motors and generators?

Answer 15

An induced EMF that opposes the applied voltage, reducing current as motor speed increases.

Question 16

What law explains back EMF?

Answer 16

Lenz’s Law – the induced current always opposes the change causing it.

Question 17

What is an eddy current?

Answer 17

Circulating currents induced in conductors by changing magnetic flux.

Question 18

How are eddy currents used in practical applications?

Answer 18

Used in induction cooktops, electromagnetic braking, and metal detectors.