Unit 2 Definitions

Question 1

Define the watt

Answer 1

The watt is the SI unit of power and is equivalent to one joule transferred per second

Question 2

State that the efficiency of a device is always less than 100% because of heat losses

Answer 2

^^

Question 3

Define the joule

Answer 3

The SI unit of work or energy and is equal to the energy transferred when one Newton is moved one meter

Question 4

electric current is: the net flow of charged particles

Answer 4

the net flow of charged particles

Question 5

The charge carriers in a metal are?

The charge carriers in an electrolyte are?

Answer 5

Electrons

Ions

Question 6

Explain what is meant by conventional current and electron flow

Answer 6

Conventional flow is from positive to negative

Electron flow is from negative to positive

Question 7

Define the coulomb

Answer 7

Charge = current x time

The coulomb is the SI unit of charge.

1 coulomb = 1 amp second

Question 8

State what is meant by drift velocity

Answer 8

Mean drift velocity is the average velocity that charge carriers (electrons) move down the wire

Question 9

Define potential difference

Answer 9

P.d. Is the energy transferred per coulomb of charge from electrical energy to other forms

Question 10

Define the volt

Answer 10

1 volt = 1 joule / 1 second

Question 11

Define EMF

Answer 11

Emf is the energy transferred by the supply, per unit charge from other forms, to electrical

Question 12

Describe the difference between EMF and Pd in terms of energy transfer

Answer 12

Emf is the energy transferred by the supply, per unit charge from other forms, to electrical

Pd is the energy transferred per coulomb of charge from electrical energy to other forms

Question 13

Define resistance

Answer 13

Resistance is a measure of the opposition a material exerts against the flow of electrons

Question 14

Define the ohm

Answer 14

1 ohm is the resistance when the ratio of p.d. Across a component to current through it is 1 volt per Amp.

Question 15

State ohms law

Answer 15

Current is an ohmic conductor is proportional to the voltage across it

(Provided temperature and other physical conditions are constant

Question 16

Define the resistivity of a material

Answer 16

Resistivity is an inherent property of a material. It depends of the atomic structure and temperature of the material.

Question 17

Define the kilowatt hour (kWh) as a unit of energy

Answer 17

1 kWh is the equivalent of 1000 watt hours
Or
3.6 mega joules

Question 18

State kirchoff’s second law and appreciate that this is a consequence of conservation of energy

Answer 18

Kirchoff’s second law:

• Based on the law of conservation of energy
• A circuit loop must contain an emf and a p.d.
• I.e. A power source and some form of component

Question 19

Explain the meaning of the term ‘terminal p.d.’

Answer 19

Terminal p.d. Is the voltage is available to the circuit (what is coming out of the battery), not just what the battery says on the tin.

Question 20

Define displacement of a wave

Answer 20

Displacement is the distance a particle moves from its central equilibrium position

Question 21

Define the amplitude of a wave

Answer 21

Amplitude is the maximum displacement from the central equilibrium position

Question 22

Define path difference

Answer 22

Path difference is the extra distance travelled by waves from one source compared to another

Question 23

Define time period of a wave

Answer 23

Time period = 1/frequency

But, the period of a wave is the time for a particle on a medium to make one complete vibration cycle.