electricity

Question 1

what is resistance

Answer 1

how much a component resists the flow of charge carriers through it
p.d/current

Question 2

What is an ohm

Answer 2

The resistance of a component when a p.d of 1v is produced per ampere of current

Question 3

What is ohms law

Answer 3

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

Question 4

Resistance of a wire is directly proportional to..

Answer 4

length

Question 5

What is a thermistor
what happens to resistance when temperature increases

Answer 5

Semiconductor with a negative temperature coefficient (resistance drops as temperature increases) - non ohmic

Question 6

rules about resistance in series and in parallel

Answer 6

series
Rt= R1 + R2 + R3
parallel
1/Rt = 1/R1 + 1/R2 + 1/R3

Question 7

kirchoffs second law

Answer 7

In any circuit, the sum of the electromotive forces is equal to the sum of the p.ds around a closed loop.

Question 8

in a series circuit the current is…

Answer 8

always the same

Question 9

how is emf shared around a series circuit

Answer 9

shared across the components. if components have the same resistance then the p.ds will be shared equally. if different the component with greater resistance will have a greater proportion of the emf

Question 10

in parallel circuit the e.m.f is

Answer 10

equal no matter how many branches there are

Question 11

what is lost volts?

Answer 11

Lost volts is when the p.d measured at the power source is less than the actual e.m.f . This is due to not all the energy transferred to the charge is available for the circuit, as some is transferred into heat.

Question 12

EMF=

Answer 12

terminal p.d + lost volts

Question 13

how does increasing current affect lost volts

Answer 13

increasing current means more work is done by the charges, increasing the lot volts - lowering the terminal p.d.

Question 14

what is a potential divider

Answer 14

varies the p.d to give any value up to the maximum e.m.f of a circuit

Question 15

what is a potentiometer

Answer 15

variable resistor with 3 terminals and a sliding contact - adjusting this varies the Vout

Question 16

diiference between p.d and e.m.f

Answer 16

Potential difference is the measure of energy (work done) by charge carriers
EMF is when work is done on the charge carriers

Question 17

what is a volt

Answer 17

the p.d \acroos a component when 1j of energy is transferred per unit charge
1v= 1JC^-1

Question 18

explain an electron gun

Answer 18

Electrons heated on a hot filament until they have enough energy to escape the surface (thermionic emission).
As there is accelerating p.d between the cathode and the anode the electrons speed towards it in a line- this creates a beam of electrons going through the hole all with similar kinetic energy

Question 19

why does when a wire get hotter, its resistance increases

Answer 19

As temperature increases, positive ions inside the wire have more internal energy and vibrate more intensely , this means collisions increase and charge carriers do more work and transfer more energy

Question 20

relationship between resistance and length

Answer 20

resistance is directly proportional to length

Question 21

resistance and temperature in a thermistor
why

Answer 21

as temp increases, resistance decreases
This is because an increase in temperature increases the number density of electrons.

Question 22

Kirchhoff second law

Answer 22

In any circuit, the sum of the electromotive forces is equal to the sum of all the p.ds

Question 23

what is a potentiometer

Answer 23

variable resistor with 3 terminals and a sliding contact. Adjusting the contact varies the p.d giving a variable Vout