A2 unit 4 Definitions

Question 1

Capacitor

Answer 1

A capacitor is a pair of conducting plates separated by an

insulator. If a potential difference is placed across the plates, they acquire equal and opposite charges.

Question 2

Capacitance

Answer 2

charge on either plates/pd between plates Q/V

Question 3

Dielectric

Answer 3

Insulator between the plates of a capacitor, also serving to make the capacitance larger than if there were just empty space.

Question 4

Newton’s law of gravitation

Answer 4

The gravitational force between two particles is proportional to the product of their masses, m1 and m2, and inversely proportional to their separation squared, r^2. F=(Gm1m2)/r^2 in which G is the gravitational constant.
G = 6.67×10^-11N m^2 kg^-2

Question 5

Coulomb’s Law

Answer 5

The electrostatic force, F, between two small bodies is
proportional to the product of their charges, Q1 and Q2, and inversely proportional to their separation squared, r^2. F=(Q1Q2)/4∏𝝴0r^2 in which 𝝴0is the permittivity of free space = 8.85x10-12 F m^-1

Question 6

Electric Field Strength, E

Answer 6

The force experienced per unit charge by a small positive

charge placed in the field. Unit: V m^-1 or N C^-1

Question 7

Gravitational field strength, g

Answer 7

The force experienced per unit mass by a mass placed in the field. Unit: m s^-2 or N kg^-1

Question 8

Electric potential, VE

Answer 8

Electric potential at a point is the work done per unit charge in bringing a positive charge from infinity to that point.
Unit: V or JC^-1

Question 9

Gravitational potential, VG

Answer 9

Gravitational potential at a point is the work done per unit
mass in bringing a mass from infinity to that point.
Unit: J kg^-1

Question 10

Kepler’s 1st law

Answer 10

Each planet moves in an ellipse with the Sun at one focus.

Question 11

kepler’s 2nd law

Answer 11

The line joining a planet to the centre of the Sun sweeps out equal areas in equal times.

Question 12

phasor

Answer 12

This is an imaginary vector rotating at the frequency, f of the alternating current. Its length can represent the rms (or peak) value of a current or a pd, or the value of a resistance or
reactance.

Question 13

impedance

Answer 13

When an AC voltage is applied to a combination of resistance and capacitance or inductance (or both), the impedance is given by Z=Vrms/Irms

Question 14

resonance frequency in LCR

Answer 14

This is the frequency of applied pd at which Irms is maximum, for a given Vrms.