Topic two - electricity Flashcards Preview

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Flashcards in Topic two - electricity Deck (28):
1

what is current

it is the rate of the flow of charge

2

what is the relationship between current and p.d. in an ohmic conductor

it is linear

3

what is the relationship between current and p.d. in a filament bulb

as the p.d. increases, the resistance increases and therefore, the gradient of the line bends towards the p.d. value

4

what is the relationship between current and p.d. in a diode

when p.d. is passed in one direction, the resistance is low. however, in the other, it is extremely high, hardly allowing any current at all.

5

how does an LDR or light dependent resistor work

as the light intensity increases, the resistance decreases

6

how does a thermistor work

as the temperature increases, the resistance decreases

7

if you wanted a heater to turn on when it is cold, how would you wire the thermister in relation to it.

you would connect it in parallel

8

if you wanted a fan to turn on when it is hot, how would you wire the termister in relation to it

you would connect it in series

9

if you wanted a light to turn on when it is dark, how would you wire the LDR in relation to it

you would connect it in parralel

10

in a series circuit, how is the p.d. distributed

you add up the p.d. over all the components and it will equal the p.d. in the cell

11

in a series circuit, how is the current distributed

it is the same at any point in the circuit

12

in a series circuit, how do you work out the total resistance

you add up the resistance in each of the components

13

in a parallel circuit, how is the p.d. distributed

it is the same in each of the branches

14

in a parallel circuit, how is the current distributed

you add the current in each branch to find the current at the cell

15

in a parallel circuit, how do you work out the total resistance

the reciprocal of the total resistance is equal to the reciprocal of each of the branches combined.

16

what is the key difference between a mains supply and a battery supply

mains is ac and battery is dc

17

which side of the socket do you plug the live pin into

the right

18

which side of teh socket do you plug the neutral pin into

the left

19

what voltage is the mains kept

230 V

20

at what frequency is the mains ac current

50 Hz

21

how do you work out the energy transferred

the charge flow x p.d.

22

how do you work out the power of an output

p.d. x current
therefore if you sub in V=IR
current squared x resistance

23

name some factors that could cause peaks in electricity demands

when people get up
when people come home from school or work
when it starts getting dark and cold outside
sporting matches

24

why must the p.d. and current be changed when conducting a large amount of electricity across the country

at a high current, far more energy is lost to heat, due to the incredibly high resistance, so in order to prevent this, the p.d. is raised using transformers and therefore, the current is decreased, limiting the heat loss.

25

what properties do materials being rubbed together have to have to become statically charged

they must be insulating.

26

how will a polythene rod become charged when rubbed with a cloth

negatively

27

how will an acetate rod become charged when rubbed with a cloth

positively

28

how are sparks caused with electrostatics

when the p.d. between the object and the earth is large enough, it will jump across the gap through the air, this causes a spark