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My Physics > Section 2: Electricity > Flashcards

Section 2: Electricity Flashcards

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1
Q

Current

A

Rate of flow of charge (usually electrons) around a complete circuit

Current is measured in amps (A) with an ammeter in series

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2
Q

Voltage

potential difference

A

Energy carried around a circuit by electrons

v = amount of energy transferred per coulomb of charge
1 v = 1 joule per coulomb

Measured in volts (v) with a voltmeter in parallel

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3
Q

Current and electrons

A

Current is always from positive to negative

Electrons in a circuit always flows away from the negative terminal to the positive

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4
Q

Battery voltage

A

Sum of voltage of all other components

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5
Q

Draw symbols for:

  • cell/battery
  • switch
  • ammeter
  • voltmeter
  • bulb
  • LDR
  • thermistor
  • resistor
  • variable resistor
A

check it

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6
Q

Equation for current

A 
current = charge / time
I = Q/t
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7
Q

Equation for voltage

A 
voltage = energy / charge
V = E/Q
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8
Q

Resistance

A

Resists the flow of the current

Measured in ohms Ω

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9
Q

Light dependent resistor

A

Resistance decreases as light increases, depends on light levels

  • In bright light, resistance is low, more current can flow through
  • In darkness, resistance is the highest

Useful for various electronic circuits e.g automatic night light and burglar detectors

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10
Q

Equation for resistance

A

resistance = voltage / current

Ω V A

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11
Q

Equation for power

A

power = voltage x current
(watts)
or joules per second

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12
Q

Thermistor

A

Resistance decreases as temp increases, depends on temp

  • low temp, resistance high
  • high temp, resistance low

Useful for temp detectors e.g fire alarms, thermostats

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13
Q

2 things for a circuit to work

A
  1. Complete circuit
    wires runs from battery all the way
  2. No short circuits
    no way past a lamp going through other components
    (otherwise lamp will not light)
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14
Q

Series Circuit

-current and voltage

A
  1. All components are connected in a line, end to end
  2. If one component is removed the circuit is broken and all stops working

-Current is the same everywhere A1 = A2 = A3

-Potential difference is shared between all components
V = V1 + V2
voltage round a series circuit adds up to voltage source

-Total resistance is the sum of all individual resistors
R = R1 + R2 + R3

  • Cell voltages add up
    e. g two 1.3 V cells in series would supply 3V in total
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15
Q

Parallel Circuit

-current and voltage

A
  1. Each component separately connected to the battery
  2. If one component is removed it doesn’t affect all others

-Current is shared between branches
A = A1 + A2
-There are junctions where current split or rejoins, total current into junction = leaving junction
-Total current = total current of separate branches

-Potential difference the same across all components
V1 = V2 = V3
-All components gets the full p.d, so identical bulbs are the same brightness

  • Resistance is always less than that of the branch with the smallest resistance
  • Resistance lower because current has more than one branch to take
  • A circuit with 2 resistors in parallel will have a lower resistance than a circuit with either of the resistors by themselves
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16
Q

Current - voltage graph for resistors

V-I graphs

A

-Current through a resistor (at constant temp) is directly proportional to the voltage (Ohms law)
- Steeper the slope, the lower the resistance
R = V / I

-x-axis : potential difference
-y-axis : current
- straight line through, x = y
(see graph)

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17
Q

V - I graph for bulbs

A
  • Bulbs do not follow ohms law
  • The resistance increases as the temp increases, so it’s not directly proportional
  • x-axis : potential difference
  • y-axis : current
  • ’s’ shape

(see graph)

18
Q

V - I graph for diodes

A
  • Used to regulate voltage in circuits and make logic gates
  • Has very high resistance in one direction, so current can only flow in other direction
  • x-axis : potential difference
  • y-axis : current
  • flat and then a steep rise

(see graph)

19
Q

What can be used to indicate the presence of a current in a circuit?

A

lamps and LEDs

20
Q

What happens to the current if I increase the resistance ?

What if i decrease it?

A

increasing resistance will decrease the current, this is achieved by adding more components or components with higher resistance

-increase the current, achieved by removing or replacing with components of a lower resistance

21
Q

Draw a series circuit

draw a parallel circuit

A

check it

22
Q

What is voltage in terms of energy transfer?

A

amount of work done per unit of charge

23
Q

What is a series circuit useful for?

A

everything is connected in a line so the voltage is shared out between components.

  • useful for low powered things like fairy lights
  • however if one component breaks then whole circuit stops working
24
Q

What is a parallel circuit useful for?

A

different components connected separately to supply

  • practical because if one component breaks the circuit still works
  • better for higher powered thing due to p.d being same for all components
  • however power supply used quickly
25
Q

What is the risk of water in domestic electricity?

A

water conducts electricity and energy from circuit can flow through it, creating a fire and electrocution risk

26
Q

What is the risk of frayed cables/damaged plugs in domestic electricity?

A

the insulation has wore down, exposing live wires, electricity can be conducted

27
Q

What is the risk of over loading in domestic electricity?

A

can cause fire

28
Q

What are the features of a plug?

Label it

A
  • plastic casing which is an insulator
  • 3 pins made from brass which is a good conductor
  • fuse between live terminal and pin. This breaks if the current is too high
  • cable secured in the plug by cabe grip, which should grip the cable itself, and not individual wires

neutral wire : blue
earth wire : green/yellow stripes
live wire : brown

29
Q

what equation connects energy, current, time and voltage

A

energy(J) = current(A) x voltage(V) x time(s)

30
Q

What is the use of the earth wire ?

A
  • many electrical appliances such as cookers, fridges have metal casing.
  • earth wires creates the path of low resistance for current to flow if live wire touches the casing so an electric shock is avoided
31
Q

What is the use of the fuse?

A
  • made from a metal that has a low melting point so if a large current flows through the circuit and the fuse wire gets very hot the metal melts which breaks the circuit
  • prevents electric shock and fires
  • needs to be replaced once used
32
Q

What are the use of circuit breakers?

A

if too large a current flows through a circuit then a switch opens making the circuit incomplete.
once fault in circuit corrected, the switch is reset by pressing a reset button

33
Q

What is the use of live wires?

A

provides the path which electrical energy from power station travels

34
Q

what equation connects power, current and voltage?

A 
power(W) = current (A) x voltage(V)
P = I x V
35
Q

How to choose the correct fuse size to be fitted to a device?

A
  • Fuses come in standard ratings of 3A, 5A and 13A
  • chose one which allows the correct current to flow but blows if it gets a bit larger
  • e.g if correct current in circuit is 4A then choose a 5A fuse
36
Q

What is the use of insulation?

A
  • covering live wire with a material that doesnt conduct
  • Double insulation is when all electrical parts of an appliance is insulated so that the user cannot touch it. e.g when an appliance has a casing made of plastic
37
Q

Prove E = IVt from V = E/Q and Q =It

A 
E = Q x V
E = (I x t) x V
E = I x t x v
38
Q

What equation connects charge, current and time?

A

charge (coulombs) = current(A) x time(s)

Q = I t

39
Q

What is Ohm’s law?

A 
V = I x R
voltage(V) = current(A) x resistance (Ω)
40
Q

How does changing resistance affect the current in a circuit?

A

Increasing the resistance will decrease the current

Decreasing the resistance will increase the current

41
Q

What’s an experiment to investigate Current and Voltage characteristics?

A

Have a circuit with a voltmeter around a lamp and an ammeter.

  • turn power supply up till p.d across lamp is 12
  • record p.d + current
  • calculate resistance r = V/I
  • change voltage to see relationship
42
Q

What is the difference between direct current (d.c) and alternating current (a.c)?

A

d. c:
- current flows in only one direction, such as when supplied by batteries and cells
- line on graph is flat

a. c:
- current constantly changes directions, such as when supplied by Mains electricity
- It has the frequency of 50 Hz, which means it changes direction, and back again 50 times a second
- line on graph like a transverse wave
- p.d of the live terminal varies between large + ve and -ve value
- p.d of neutral terminal is close to 0
- although the mean voltage is about 230 V, the peak voltage is higher

My Physics (12 decks)

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