Electricity Flashcards Preview

BMAT: Physics > Electricity > Flashcards

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

how do transformers work?

primary coil generates magnetic field which stays in iron core
- AC supply in primary coil causes changing magnetic field
- magnetic field induces alternating p.d. in secondary coil
if step up pd. is greater (more turns) / vice versa