Flashcards in Electricity Deck (33):

1

## how is static electricity formed?

### charging of insulators by friction

2

## how are positive and negative charges formed?

### movement of electrons from one material leaves positive charge and produces negative charge on material gaining electrons

3

## how does static electricity occur by rubbing rod with cloth?

###
- with polythene rod, cloth transfers electrons onto rod

- with acetate rod, electrons are transferred onto cloth

4

## name three uses of static electricity

###
- paint sprayers

- defibrillators

- dust precipitators

5

## how do paint sprayers work?

###
- paint gun is charged which charges paint

- paint drops repel each other giving fine spray of paint

- object is opposite charge so attracts fine spray of paint all over equally

6

## how do dust precipitators work?

###
cleans up emissions from chimney

dust passes through charged grid

atttact to metal plates so then no pollutants released to air

7

## what is the main danger of electrostatics?

### large build up of charge produces sparks

8

## how can sparks be prevented?

### earthing so charged object is connected to ground using a conductor so easy route for charge to go straight into ground without causing a build up

9

## what is current

### flow of charge

10

## formula for current

### current = charge/time

11

## units of current:

### A - amperes

12

## units of charge:

### C - coulombs

13

## what is voltage

### amount of energy transferred per unit of charge

14

## what is another term for voltage

### potential difference

15

## formula for voltage

### voltage = energy/ charge

16

## units of voltage

### volts

17

## formula for resistance

### resistance = voltage/ current

18

## units for resistance

### ohms

19

## how does current vary with voltage through a fixed resistor?

### directly proportional

20

## describe curve on V-I graph for a filament lamp

### s- shaped curve

21

## how does resistance link with temperature

### resistance increases with temperature because as electrical energy is converted to heat energy the ions vibrate more so current cannot flow as easily hence resistance increases

22

## how is voltage and current distributed in a series circuit?

###
- V: shared

- I: same

23

## how is voltage and current distributed in a parallel circuit?

###
- V: same

- I: shared

24

## how is resistance calculated in series and parallel circuits?

###
series: adds up

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

25

## what is power?

### how much energy transferred per second

26

## unit of power

### watts

27

## formula for power

### current x voltage

28

## formula for energy transferred

### power x time

29

## what is electromagnetic induction?

### creation of p.d. across a conductor experiencing a changing magnetic field

30

## how do ac generators work?

###
rotating coil in magnetic field - every half turn current changes direction

- higher current when coil is perpendicular to field

31

## factors affecting induced voltage

###
- number of turns

- speed of turns

- cross-section of coil

- strength of magnetic field

32

## formulas for step up/down transformers

###
Vp Ip = Vs Is (power in = power out) as a consequence of 100% efficiency

Vp/Vs = Np/Ns

33