Electrons, Waves and Photons

Question 1

Define the electronvolt

Answer 1

the energy transferred by an electron travelling through a potential difference of 1V

Question 2

Define the ohm

Answer 2

the resistance when 1 volt of potential difference produces 1 ampere of current

Question 3

Define the kilowatt-hour

Answer 3

the energy transferred by a 1kW device in an hour

Question 4

Define number density

Answer 4

number of charged particles per unit volume

Question 5

Equation of resistivity

Answer 5

Resistance x (Cross-sectional Area/Length)

Question 6

Define Potential difference and e.m.f

Answer 6

P.d: energy transferred per unit charge from electrical energy into other forms
electromotive force: energy transferred per unit charge into electrical energy from other forms

Question 7

What is internal resistance?

Answer 7

the resistance to the flow of current inside the power supply itself. Some energy is lost as heat inside a cell

Question 8

What is the terminal p.d.?

Answer 8

potential difference measured across the terminals of an em.f source

Question 9

Define displacement (waves)

Answer 9

distance moved from equilibrium of a point on a wave, 1d vector (positive or negative)

Question 10

Define wavelength

Answer 10

the distance between two adjacent peaks and troughs

Question 11

Define phase difference

Answer 11

the fraction of a cycle between the oscillations of two particles (measured in degrees or radians)

Question 12

Define path difference

Answer 12

The difference in the distances traveled by two waves which are coherent at a particular point

Question 13

Define work function

Answer 13

minimum energy to release an electron from the surface of a metal

Question 14

Define threshold frequency

Answer 14

the minimum frequency of electromagnetic radiation that will release an electron from the surface of a metal

Question 15

What way is conventional current vs electron flow?

Answer 15

Conven. positive->negative

electrons negative->positive

Question 16

Kirchoff’s first law

Answer 16

sum of current into a junction equals the sum of current out, charge is conserved

Question 17

Kirchoff’s second law

Answer 17

sum of e.m.fs around a loop = sum of p.d.s around the same loop; energy is conserved

Question 18

Define mean drift velocity

Answer 18

average speed of charged particles along the length of a conductor

Question 19

What is Ohm’s law?

Answer 19

for a metallic conductor at a constant temperature, the voltage is proportional to the current

Question 20

What is a progressive wave?

Answer 20

a transfer of energy as a result of oscillations