Electricity

Question 1

Ohms law

Answer 1

‘For metals at a constant temperature, the current in the metal is proportional to the potential difference across it’

Question 2

Electon Charge

Answer 2

e = -1.6 x 10^-19 C
Charge = Number of charge carriers x Charge on one carrier

Question 3

Current

Answer 3

‘the rate of flow of positive charge’ (A)

Question 4

Potential difference

Answer 4

The work done per coulomb of charge passing a point (V)

The energy transferred from the charge

Question 5

EMF

Answer 5

The energy transferred to each coulomb of charge at a source
The energy transferred to the charge

Emf = Current x Internal resistance + Current x terminal resistance (V)

Question 6

Resistance

Answer 6

The ratio of potential difference to current accros a component (Ohms)

Question 7

Power

Answer 7

The rate of change of Work done

Question 8

Electrical work

Answer 8

Work Done = Potential Difference x Current x time

Question 9

Resistivity

Answer 9

Resistivity = (resistance x Cross-Sectional area) / Length of wire (Ohm Meteres)

Question 10

Current in series

Answer 10

On a single branch (or loop) of a circuit, the current is the same all the way around

Question 11

Current in parallel

Answer 11

At a junction (or branching) of a circuit, the current is shared inversely proportional to the resistance of each branch.

Question 12

Potential difference in Series

Answer 12

Components connected in series along a branch (or loop) will share the supplied potential difference in proportion to their resistances (i.e. more p.d. across components with higher R)

Question 13

Potential difference in Parallel

Answer 13

In parallel, each branch (or loop) has the same potential difference supplied across it.

Question 14

Resistance in series

Answer 14

Rtotal = R1 + R2 + …

Question 15

Resistance in parallel

Answer 15

1/Rtotal = 1/R1 + 1/R2 + …

Question 16

Drift Velocity

Answer 16

Speed at which a charge carrier moves through a conductor when a current flows. (ms-1)
Speed in metals: 0.1 mms-1

Question 17

Charge carrier density

Answer 17

“The number of charge carriers per unit volume” (m-3)

Question 18

Semiconductors

Answer 18

Have a lower amount of free electrons, so have higher resistances.
When temperature increases in a thermistor, the atoms in the material release more electrons, due to an increase in thermal energy of the electrons, causing a decrease in resistance. This causes an increase in current. There is also an increse in the amplitude of the lattice Ion vibrations, increaseing the resistance but the current increase outweighs this.
In a Light Dependant Resistor (LDR) Light decreases the resistance by releasing more electrons and increasing the amplitude of the lattice ion vibrations.

Question 19

Conductors

Answer 19

Have a large amount of free electrons, so have low resistances.
When temperature increases in a conductor, the amplitude of the lattice ion vibrations increases, causing an increase in resistance. This causes a decrease in current.

Question 20

Insulators

Answer 20

Have a very low amount of free electrons, so have high resistances.
When temperature increases in an insulator, the amplitude of the lattice ion vibrations increase, causing an increase in resistance. This causes a decrease in current

Question 21

Internal resistance

Answer 21

The resistance inherent to an emf source or power supply. Causes a dissipation of energy inside the source, and so there is some p.d. wasted or ‘lost’
Internal resistance = ‘Lost volts’/Current (Ohms)

Question 22

‘lost volts’

Answer 22

The p.d. dissipated (as heat) inside a source or power supply due to its internal resistance, r.
‘Lost Volts’ = Current x Internal resistance (V)

Question 23

Terminal potential difference

Answer 23

The p.d. available to a circuit, once some has been lost due to the internal resistance of the source. This is the p.d. that is measured across the terminals of a power source (Ohms)

Question 24

Potential divider

Answer 24

A circuit that consists of two (or more) resistors (R1, R2, …) in series that share a potential difference between them. Since the current through each resistor is the same:
VTOT / RTOT = V1 / R1 = V2 / R2 = V3 / R3 …

Question 25

Potentiometer

Answer 25

A component that divides potential into two (like two resistors R1 & R2) with a fixed total resistance, so that R1 + R2 = RT. The current through a potentiometer is always the same.