electric circuits

Question 1

Define electricity

Answer 1

Electricity is a flow of electrons around a circuit

Question 2

Define potential difference

Answer 2

The change in potential energy per unit charge between two points, due to the charge doing work on circuit components

Question 3

Define electromotive force

Answer 3

The change in electric potential energy per unit charge between two points, due to work being done on the charge, for example by a battery or a power supply

Question 4

Kinetic energy of electrons

Answer 4

When a potential difference accelerates a charged particle, the energy transferred is equal to the kinetic energy gained by the particle (usually an electron). KE=1/2mv*2

Question 5

What are volts

Answer 5

1 volt is the potential difference between two points when a 1 C charge passing between the points experiences a change in electric potential energy of 1 J

Question 6

difference between emf and pd

Answer 6

p.d is used when charge carriers transfer energy to the component, into another store, eg. light or heat. e.m.f is used when work is done on the charge carriers, gaining energy from light, heat or chemical stores and beinhg transferred into electrical energy.

Question 7

what does an electron gun do?

Answer 7

creates a small beam of electrons, used in instruments such as electron microscopes, mass spectrometers and oscilloscopes

Question 8

how do electron guns work

Answer 8

electrons from a metal filament are heated and escape from the surface of the metal (thermionic emission) and accelerate towards the anode. The anode has a small hole, so the electrons are fired through it and create a beam

Question 9

What is thermionic emission

Answer 9

the emission of electrons through the action of heat

Question 10

order of centi, milli etc

Answer 10

terra
giga
mega
kilo

centi
milli
micro
nano
pico
temto

Question 11

What is resistance

Answer 11

It takes energy to push electrons through a component. The higher the resistance, the more energy it takes. Resistance is the ratio of voltage and current

Question 12

what is ohms law

Answer 12

for a metallic conductor at a constant temperature, the current in the wire is directly proportional to the p.d.

Question 13

what can you draw from an I/V graph of a resistor?

Answer 13

-p.d is directly proportional to current
-obeys ohms law (is an ohmic conductor)
-resistance is constant
-resistor behaves the same way regardless of polarity

Question 14

what can you draw from an I/V graph of a filament lamp?

Answer 14

-p.d is not directly proportional to current
-doesnt obey ohms law (isnt an ohmic conductor)
-resistance is not constant
-behaves the same way regardless of polarity

Question 15

What is electrical power

Answer 15

Power is the rate at which energy is transferred, used or transformed, measured in J s-1 or Watts.

Question 16

what is a kilowatt hour

Answer 16

A unit of energy equal to 1kW of power usage for 1 hour i.e. 1kWh = 1000 x 60 x 60 = 3.6 million joules. Often used to calculate

Question 17

what is a thermistor

Answer 17

An electrical component that has a resistance that decreases as the temperature increases

Question 18

what is resistivity

Answer 18

A property of a material, measured in Ω m. ρ = RA/l where ρ = resistivity (in Ohm.metres (Ω⋅m)), R = resistance (in Ohms), A = area (in m2) and l = length of wire (in m).

Question 19

What is internal resistance

Answer 19

Opposition to charge within a source of e.m.f

Question 20

What are lost volts

Answer 20

The difference between terminal voltage and e.m.f within a source of e.m.f due to energy being dissipated across the internal resistance (usually from heating)

Question 21

what is terminal p.d

Answer 21

The potential difference measured across the battery/power supply when that battery/power supply is connected by a complete circuit to a load (external) resistance. If there is no internal resistance, the terminal p.d. will equal to the e.m.f

Question 22

what is a potentiometer

Answer 22

A potential divider circuit which consists of one length of wire and a sliding connection to alter the ratios resistances of the two sections of wire