Electricity

Question 1

how is static electricity formed?

Answer 1

charging of insulators by friction

Question 2

how are positive and negative charges formed?

Answer 2

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

Question 3

how does static electricity occur by rubbing rod with cloth?

Answer 3

• with polythene rod, cloth transfers electrons onto rod

- with acetate rod, electrons are transferred onto cloth

Question 4

name three uses of static electricity

Answer 4

• paint sprayers
• defibrillators
• dust precipitators

Question 5

how do paint sprayers work?

Answer 5

• 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

Question 6

how do dust precipitators work?

Answer 6

cleans up emissions from chimney
dust passes through charged grid
atttact to metal plates so then no pollutants released to air

Question 7

what is the main danger of electrostatics?

Answer 7

large build up of charge produces sparks

Question 8

how can sparks be prevented?

Answer 8

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

Question 9

what is current

Answer 9

flow of charge

Question 10

formula for current

Answer 10

current = charge/time

Question 11

units of current:

Answer 11

A - amperes

Question 12

units of charge:

Answer 12

C - coulombs

Question 13

what is voltage

Answer 13

amount of energy transferred per unit of charge

Question 14

what is another term for voltage

Answer 14

potential difference

Question 15

formula for voltage

Answer 15

voltage = energy/ charge

Question 16

units of voltage

Answer 16

volts

Question 17

formula for resistance

Answer 17

resistance = voltage/ current

Question 18

units for resistance

Answer 18

ohms

Question 19

how does current vary with voltage through a fixed resistor?

Answer 19

directly proportional

Question 20

describe curve on V-I graph for a filament lamp

Answer 20

s- shaped curve

Question 21

how does resistance link with temperature

Answer 21

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

Question 22

how is voltage and current distributed in a series circuit?

Answer 22

• V: shared

- I: same

Question 23

how is voltage and current distributed in a parallel circuit?

Answer 23

• V: same

- I: shared

Question 24

how is resistance calculated in series and parallel circuits?

Answer 24

series: adds up
parallel: 1/Rt= 1/R1 + 1/R2 + 1/R3

Question 25

what is power?

Answer 25

how much energy transferred per second

Question 26

unit of power

Answer 26

watts

Question 27

formula for power

Answer 27

current x voltage

Question 28

formula for energy transferred

Answer 28

power x time

Question 29

what is electromagnetic induction?

Answer 29

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

Question 30

how do ac generators work?

Answer 30

rotating coil in magnetic field - every half turn current changes direction
- higher current when coil is perpendicular to field

Question 31

factors affecting induced voltage

Answer 31

• number of turns
• speed of turns
• cross-section of coil
• strength of magnetic field

Question 32

formulas for step up/down transformers

Answer 32

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

Question 33

how do transformers work?

Answer 33

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