P4 - Electricity

Question 1

electric field

Answer 1

region in which an electric charge experiences a force

Question 2

for a positive charge, what direction would the force be experienced?

Answer 2

outwards

Question 3

for a negative charge, what direction would the force be experienced?

Answer 3

inwards

Question 4

electric current

Answer 4

charge passing a point pre unit time

Question 5

electrostatic charge

Answer 5

materials’ charge

Question 6

where does electric charge come from?

Answer 6

batteries and generators / if rubbed

Question 7

what 2 materials can used to create charge?

Answer 7

polythene (becomes -ve) and perspex (becomes +ve)

Question 8

closer the charges, _____ the _____ between them

Answer 8

greater force

Question 9

what does rubbing materials do?

Answer 9

seperates charges that are already there

Question 10

conductors and examples?

Answer 10

materials that let electrons pass through them as they have free electrons between indivisual atoms
-ex copper, gold, metals, carbon

Question 11

insulators and examples?

Answer 11

materials that dont conduct as electrons are tightly held by atoms and are not free. (but it can be transferred by rubbing and once transferred, it stays. and its easy to charge)
-ex: plastics, glass, dry air

Question 12

semi-conductors and examples?

Answer 12

materials that are poor conductors when cold, good conductors when warm
-ex: silicon, germanium

Question 13

direction of conventional current? flow of electrons?

Answer 13

positive to negative / negative to positive

Question 14

earthing

Answer 14

connected to the ground by conducting materials so that unwanted charges flow away. if this is not done, electrons may be pulled through the air and cause dangerous sparks

Question 15

voltage

Answer 15

cause of current in the circuit

Question 15

induced charges

Answer 15

appear on an unchanged object because there’s a charged object nearby (opposite charges)

Question 16

what can electrostatic charge be detected by?

Answer 16

leaf electroscope

Question 17

static electricity

Answer 17

charges that are not free to move (build up in one place, shock when they move) (build up of charge on insulating materials)

Question 18

static electrcity uses [3]

Answer 18

-electrostatic smoke precipitators (dust attracts to the charged plates)
-spray painting (spray drop is +ve, drops repela and spread out, earth is -ve and the car is connected to earth, drops attracted to the car)
-photocopiers (black toner attracted to paper)

Question 19

emf

Answer 19

electricatl work done by a source in moving a unit charge around a complete circuit (V) (across cell)

Question 20

pd

Answer 20

work done by a unit charge passing between two points in a circuit (V) (across device)

Question 21

resistance

Answer 21

ratio of voltage to current in an appliance (measures load)

Question 22

how to measure emf?

Answer 22

voltmeter across cell

Question 23

how to measure pd?

Answer 23

voltmeter across appliance (device)

Question 24

if resistance is greater, what happens to voltage and current?

Answer 24

resistance increases, voltage increases, current decreases

Question 25

resistance formula

Answer 25

voltage / current

Question 26

current formula

Answer 26

charge / time (I=Q/t)

Question 27

what is Ohm's law?

Answer 27

current is directly proportionate to Voltage (V increases, I increases)

Question 28

what are ohmic conductors? examples? graph?

Answer 28

conductors that follow Ohm's law -examples: metallic conductors at room temperature -I-V graph is a straight line through the origin

Question 29

Non-Ohmic conductors? graph?

Answer 29

conductors that don't follow Ohm's law -I-V graph is not a straight line through the origin

Question 30

relation between length and resistance

Answer 30

resistance is directly proportionate to length (longer the wire, more resistance)

Question 31

relation between area and resistance

Answer 31

resistance is inversely proportionate to area (thin wire, large resistance / thick wire, small resistance)

Question 32

what happens to resistance if area doubles?

Answer 32

resistance halves

Question 33

what happens to resistance if radius doubles?

Answer 33

decreases by 4 times

Question 34

formula for volts

Answer 34

energy / charge (coulombs)

Question 35

formula for energy

Answer 35

(voltage x current = power) x time

Question 36

formula for power (energy)

Answer 36

energy / time

Question 37

formula for power (voltage)

Answer 37

voltage x current (amps)

Question 38

unit for energy (power flow with time)

Answer 38

kilowatt-hour (kwh)

Question 39

what is a variable resistor

Answer 39

helps introduce varying resistance in the circuit

Question 40

HOW DOES LIGHT DEPENDANT RESISTOR AFFECT RESISTANCE?

Answer 40

LIGHT INTENSITY INCREASES, RESISTANCE DECREASES (DARK = MORE RESISTANCE) (CURVED LINE C ON GRAPH THOUGH)

Question 41

what do electric circuits do?

Answer 41

transfer energy from a source of electrical energy (electrical cell or mains supply) to the circuit components and then into the surroundings

Question 42

total resistance of series circuit

Answer 42

R1 + R2 + R3

Question 43

4 features of series circuit

Answer 43

-voltage is divided -if one disconnects all don't work -current is the same anywhere (ampmeter) -V1 + V2 + V3 = supply voltage (EMF)

Question 44

total resistance in parallel circuit

Answer 44

1/R1 + 1/R2 -total resistance is less than smallest resistance (each resistor)

Question 45

5 features of parallel circuit

Answer 45

-current splits up in proportion do resistance in each branch (larger resistance, larger current) --> I1 + I2 = I -each branch gets same voltage as supply -used in domestic wiring -if one disconnects, others still work -current from source is larger than current in each branch

Question 46

short circuit

Answer 46

huge current goes through (no resistor) and could cause a fire