11: Electromagnetic induction, capacitors, magnets

Question 1

Lenz’s law

Answer 1

The induced emf in a wire moving through a magnetic current will oppose the motion of the movement. This can then be used to find the direction of current(LHR)

Question 2

epsilon means?

Answer 2

electromotive force

Question 3

Magnetic field strength, B(T)

Answer 3

A measure of number of parallel magnetic field lines pass through a unit area(T)

Question 4

Magnetic flux density

Answer 4

A measure of number of parallel magnetic field lines pass through a unit area(T)

Question 5

Magnetic flux

Answer 5

A measure of how many parallel magnetic field lines pass through an area, ie an enclosed coil

Question 6

What affects the total flux linkage in a coil?

Answer 6

The number of turns(direct proportion), B, A, the angle between the coil and the magnetic field

Question 7

Faraday’s law?

Answer 7

Ɛ =rate of change in magnetic flux over time

Ɛ=-N(dflux/dt)

Question 8

magnetic flux in a rotating coil?

Answer 8

NBAcos(wt)

Question 9

Magnetic flux linkage. What is it measured in?

Answer 9

the number of mag lines passing through coil multiplied by no. loops. (flux x N)

Measured in Tesla-WEber per square metre

Question 10

What is the ratio of voltage out to voltage in for a transformer?

Answer 10

The same as the ratio of number of turns out to in.

Question 11

What is the ratio of current out to voltage in for a transformer?

Answer 11

The inverse of the ratio of number of turns out to in.

Question 12

what are the sources of energy loss in a transformer?

Answer 12

Heat, Eddy-currents(solved by layering and insulating), magnetic hysteresis

Question 13

Define capacitance

Answer 13

The measure of charge stored per volt

Question 14

half wave rectification

Answer 14

using a diode to ignore the ‘negative’ power. This halves the efficiency of the source

Question 15

Full wave rectification

Answer 15

Using four diodes to provide two paths for current to take so the load gets a power that is always positive

Question 16

How do you use a capacitor to smooth power out put of a rectified source?

Answer 16

You place the capacitor in parallel to the load in the circuit, so that the discharging of the capacitor becomes a temporary source of power between peaks

Question 17

What is the effect of the dielectric in a capacitor?

Answer 17

Dielectrics have dipoles. When in a capacitor, the dipoles rotate, so the side close to the positive plate becomes negative and vice versa. This lessens the push of the capacitor’s plates to each other.