Electricity and magnetism

Question 1

Coulomb’s law

Answer 1

states that any two point charges exert an electrical force on each other that is proportional to the product of their charges and inversely proportional to the square of the distance between them.

Question 2

Electric potential

Answer 2

at a point is equal to the work done in bringing unit positive charge from infinity to that point.

Question 3

Capacitance

Answer 3

is the charge stored per unit potential difference across the capacitor.

Question 4

1 farad (F)

Answer 4

is the capacitance of a capacitor that has a potential difference of 1 volt across the plates when there is a charge of 1 coulomb on the plates.

Question 5

Inverting input

Answer 5

gives an output signal that is 180◦ out of phase with the input signal.

Question 6

Non-inverting

Answer 6

input gives an output signal that is in phase with the input signal.

Question 7

Impedance

Answer 7

is similar to resistance but takes into account the effect of capacitors and inductors in an a.c. circuit.

Question 8

Bandwidth

Answer 8

is the range of frequencies that are amplified by the same factor to get a faithful reproduction of the input signal.

Question 9

Slew rate

Answer 9

is a measure of how quickly the output changes with respect to the input.

Question 10

Flux density

Answer 10

is numerically equal to the force per unit length on a straight conductor carrying unit current at right angles to the field.

Question 11

1 tesla (T)

Answer 11

is defined as the magnetic flux density that, acting normally to a straight conductor carrying a current of 1 A, causes a force per unit length of 1 N m-1.

Question 12

Electronvolt

Answer 12

is a unit of energy equal to the energy gained by an electron when it is accelerated through a potential difference of 1 volt.

Question 13

Magnetic flux

Answer 13

is the product of magnetic flux density and the area, normal to the field, through which the field is passing.

Question 14

1 weber (Wb)

Answer 14

is the flux that passes through an area of 1 m2 when the magnetic flux density is 1 T.

Question 15

Faraday’s law of electromagnetic induction

Answer 15

states that the induced e.m.f. is proportional to the rate of change of magnetic flux linkage.

Question 16

Lenz’s law

Answer 16

states that the direction of the induced e.m.f. is always in such a direction so as to produce effects to oppose the change that is causing it.

Question 17

R.m.s. value

Answer 17

of the current (or voltage) is the value of direct current (or voltage) that would convert energy at the same rate in a resistor.

Question 18

Time constant

Answer 18

is the time taken for the charge to fall to 1/e of the original charge.