physics flash cards

Question 1

Electric current

Answer 1

Electric current is the net flow of any electrically charged particles

Question 2

Electrons

Answer 2

Electtrons are the particles that there is a ‘netflow’ of when an electric current is flowing through a metal

Question 3

Ions

Answer 3

Ions are teh particles that there is a ‘netflow’ of when an electric current is flowing through ann electrolyte

Question 4

Coulomb

Answer 4

One coulomb is the charge moved when a current of on amp flows for one second of time through a point in a circuit

Question 5

Kirchhoff’s first law

Answer 5

The sum of the currents entering any junction in a circuit is equal to the sum of currents leaving that same junction because of the conservation of charge

Question 6

Mean drift velocity

Answer 6

Mean drift velocity is the average displacement per unit time with which charge carriers move in the direction of convectional current flow

Question 7

Potential difference

Answer 7

Potential difference is energy transferred (to other forms) per unit charge

Question 8

Volt

Answer 8

When 1J of energy is tranferred (to other forms) per Coulomb of charge, the p.d across 2 points is 1 Volt

Question 9

Voltmeter

Answer 9

Are connected in parallel with the circuit. they have a high resistance so that they do not unduly disturb the circuit to be measureed

Question 10

e.m.f

Answer 10

e.m.f is the electrical potential energy gained by charges, per unit charge, (across two points in a circuit).

Question 11

Differences between e.m.f and p.d in terms of energy

Answer 11

e. m.f:work done on charges (charges gain electrical potential energy),across 2 points,per unit charge
p. d:work done by charges (charges transfer electrical potential energy to other forms), across 2 points, per unit charge

Question 12

Resistance

Answer 12

Resistance is ratio of p.d across a component to the current through the component

Question 13

Ohm

Answer 13

1 Ohm is defined as the resistance of a component when a constant p.d of 1Volt, applied across the component, produces through the component a current of 1 ampere

Question 14

Ohm’s law

Answer 14

For a metallic conductor at a constant temperature, the current through the conductor is directly proportional to the p.d across it’s end

Question 15

Resistivity of metal

Answer 15

The increases resistance of metal with temperature leads to an increase in the resistivity.Caused by thr ions vibrationg more and hinder the flow of electrons. Resistivity of a metal is proportional to the temperature

Question 16

Resistivity of semi-conductor

Answer 16

The resistivity decreases as the temperature increases for a semi-conductor. Caused as more charge carriers become available.Resistivity of a semi-conductors is inversely proportional to the temperature

Question 17

Power

Answer 17

Power is the rate of energy transferred (work done)

Question 18

Fuse

Answer 18

Fuse is a deliberatley weak link in a circuit so that if the current exceeds their value it will overheat ,melt and break the circuit

Question 19

3 reasons for a fuse

Answer 19

1) To prevent fires-by providing a weak link they guarante the wire will melt first at the fuse in a safe area and not cause a fire
2) To prevent damage-again the weeak link should be lower (current wise) than any sensitive parts of the electrical applience.
3) To prevent outer case becoming live- if the outer case becomes live via a lose cable then this will result in a large current flowing [combination with earth wire] and below the fuse

Question 20

Determine the correct fuse for a electrical device

Answer 20

find the current and round up to the nearest whole value

Question 21

Kwh

Answer 21

when an electrical device , power rating of 1kw, is operating for a time of 1 hr, the energy transferes is 1Kwh

Question 22

Kirchhoff’s 2nd law

Answer 22

The sum of the e.m.f’s in a loop equals the sum of the p.d’s in that same loop. This is a consequence of conservation of energy

Question 23

Terminal p.d

Answer 23

is the potential difference across the terminals of a power supply. If the circuit is open and therefore no current is flowing this will be equal to the e.m.f.

Question 24

Progressive wave

Answer 24

Travel through material or a vacum.Transfer energy from one position to another eg Mechanical/Longitudinal/Transverse

Question 25

Mechanical wave

Answer 25

Waves which need a medium through which to travel eg sound/seismic/water

Question 26

Longitudinal waves

Answer 26

The particles of the madianoscilate parallel to the direction of wave velocity eg sound (cannot travel through a vacum)

Question 27

Transverse waves

Answer 27

The particles of the medium oscillate perpendiculary to the direction of wave velocity eg electromagnetic waves (no medium is needed; they can travel through a vacum