Electricity

Question 1

what is an electric current?

Answer 1

flow of charge

Question 2

what is charge measured in?

Answer 2

coulombs

Question 3

what is the direction of electron flow?

Answer 3

negative to positive`

Question 4

what is a conventional current?

Answer 4

positive to negative

Question 5

what is p.d.?

Answer 5

gain/loss of energy per coulomb of charge moving through an object

Question 6

when charges move through battery…

Answer 6

they gain potential energy

Question 7

when charges move through bulb…

Answer 7

they give up potential energy

Question 8

what is current?

Answer 8

number of coulombs passing through fixed point per second

Question 9

how does a bulb work?

Answer 9

converts electrical energy into light

Question 10

how does a variable resistor work?

Answer 10

converts electrical energy into heat

Question 11

rule of p.d.

Answer 11

p.d. is always conserved

Question 12

p.d. in series circuits

Answer 12

• p.d. shared between compononents

- some may be lost to wire

Question 13

p.d. in parallel circuits

Answer 13

• p.d. same for battery and bulbs

Question 14

rule of current

Answer 14

current is conserved - total current flowing in is equal to total current flowing out

Question 15

current in series circuits

Answer 15

same everywhere in circuit

Question 16

current in parallel circuits

Answer 16

shared between bulbs

Question 17

what is resistance?

Answer 17

measure of how hard it is for current to flow through a component

Question 18

how is resistance related to length?

Answer 18

directly proportional
(longer wire - higher resistance)

Question 19

how is resistance related to area?

Answer 19

indirectly proportional

thinner wire - higher resistance

Question 20

how is a resistor designed?

Answer 20

to have a constant resistance (obeys ohm’s law)

Question 21

characteristics of voltage-current graph of resistor

Answer 21

linear: current is directly proportional to resistance
high resistance - low currrent - (shallow)
low resistance - high current - (steep)

Question 22

characteristics of voltage-current graph of bulb

Answer 22

• gradient becomes less steep as current increases
  because resistance increases as temperature increases (in a metal)
• graph curves when bulb reaches working current/temp

Question 23

how is a diode designed?

Answer 23

• to make sure current only flows one way (low voltage used to prevent overheating)
• turns A.C. into D.C

Question 24

characteristics of voltage-current graph of diode

Answer 24

when voltage is negative, no current is let through (reverse biased)
when voltage is above 0.7 V, resistance drops so current flows through - steep gradient (forward biased)

Question 25

what happens to the resistance when light input increases? (in a LDR)

Answer 25

decreases

Question 26

why does resistance decrease when light input increases? (in a LDR)

Answer 26

electrons gain energy

move more easily

Question 27

what happens to the resistance when heat increases? (in a thermistor)

Answer 27

decreases

Question 28

why does resistance decrease when heat increases? (in a thermistor) when heat increases? (in a thermistor)

Answer 28

electrons gain energy

move more easily

Question 29

uses of LDR

Answer 29

• light sensors
• burglar alarms
• car headlamps
• streetlights
• cameras

Question 30

uses of thermistor

Answer 30

• fridges

- ovens