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Physics - IGCSE > Ch 18 - (Electrical Quantities ) > Flashcards

Ch 18 - (Electrical Quantities ) Flashcards

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1
Q

Define current.

A
  • Amount of charge passing a point in a circuit every second
  • charge per sec
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2
Q

What is the equation in which change, current and time are related?

A

Charge = current x time

Q = I x t

Q = charge (coulombs, C)

I = current (amps, A)

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3
Q

What is electric current?

A

flow of charge

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4
Q

What are the 2 types of current?

A
  1. Direct current
  2. Alternating current
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5
Q

Define direct current.

A
  • electrons flow in one direction only from negative terminal to positive terminal
  • produced when using dry cells and batteries
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6
Q

Define alternating current.

A
  • comes from main electricity generators
  • direction of electron flow charge changes direction regularly
  • typical frequency for the reversal of ac currents, in mains electricity is 50 Hz
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7
Q

How is current measured?

A

Using ammeters

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8
Q

How should ammeters connected?

A

In series with part of circuit

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9
Q

What does ammeter do?

A
  • Amount of charge passing through them per unit time
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10
Q

What are the 2 types of ammeters?

A
  1. Digital (with an electronic read out)
  2. Analogue (with a needle and scale )
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11
Q

What is the range of analogue ammeters?

A

1.0 - 5.0 A

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12
Q

What are the two errors possible for analogue ammeters?

A
  1. Zero error
  2. Parallax error
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13
Q

What do digital ammeters do?

A
  • measure very small currents in mA
  • displays accurate values
  • easy to use
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14
Q

What are the errors and issues with digital ammeters?

A
  • May flicker
  • zero error
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15
Q

How do metals conduct electricity?

A

flow of electrons

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16
Q

What is the charge of electrons

A

negative

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17
Q

How do electrons flow?

A

Negative to positive

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18
Q

How does conventional current flow?

A

Positive to negative

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19
Q

What is electromotive force?

A

Name given to potential difference of power source in a circuit

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20
Q

Define electromotive force.

A

The electrical work done by a source in moving a unit charge around a complete circuit.

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21
Q

What is e.m.f. measured in?

A

Volts (v)

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22
Q

What is the symbol equation of e.m.f?

A

E = W / Q

E = electromotive force (V)

W = charged from power source (J)

Q = charge on each carrier (C)

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23
Q

What does potential difference help in?

A
  • light bulb lights up
  • related to amount of energy transferred between the 2 points
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24
Q

Define potential difference.

A

the work done by a unit charge passing through a component

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25
Q

What is the unit of potential difference?

A

Volts ()V

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26
Q

What is the equation for p.d. ?

A

V = W / Q

V = potential difference (V)

W = energy from charge carriers (J)

Q = charge on each carrier (C)

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27
Q

How is potential difference measured?

A

Voltmeter

28
Q

What are the 2 ways in which potential difference is measured?

A
  1. Digital (with an electronic read out)
  2. Analogue (with a needle and scale )
29
Q

How are voltmeters connected?

A
  • parallel to wires
  • measure potential difference between 2 points
30
Q

what are the errors likely to be found in analogue voltmeter?

A
  • Parallax error
  • zero error
    0 - 5.0 V is range
31
Q

What are the errors likely to be found in digital voltmeters?

A

zero error

32
Q

What is Ohm’s law?

A

Resistance is the opposition to current

33
Q

What are resistors in circuits used for?

A

To control current

34
Q

What is the unit of resistance?

A
  • ohm
  • represented by Greek symbol ohms
35
Q

What is the equation for ohm’s law?

A

R = V / I

R = Resistance (ohms)

V = potential difference (volts, V)

I = current (amperes, A)

36
Q

What are resistors in circuits used to control?

A
  • Current in branches
  • potential difference across components
37
Q

What are the consequences of Ohm’s law?

A
  • current in electrical conductors decreases as its resistance increases
  • p.d. across an electrical conductor increases as resistance increases
38
Q

What happens as potential difference across a component is increased?

A

Current component also increases

39
Q

How is the relationship between voltage and current shown?

A

By IV graph

40
Q

How is the IV graph of a resistor ?

A

the current is proportional to the potential difference

  • resistor has a constant resistance
41
Q

How is the IV relationship for the lamp?

A

The current increases at a proportionally slower rate than the potential difference

42
Q

Why is the relationships s such for the IV of a graph?

A
  • current causes filament in lamp to heat up
  • as filament gets hot, its resistance increases
  • this opposes the current, causing it to increase at a slower rate
43
Q

what happens in reverse for diode?

A
  • High resistance
  • no current flaws
  • reverse bias
43
Q

What is a diode?

A
  • Non - ohmic conductor
  • flow only in 1 direction
  • shown by triangular arrows of diode
  • forward bias
44
Q

How is the IV graph for a diode?

A
  1. Forward bias: Sharp increase in voltage and current (on right side)
  2. Reverse bias: Flat line with current and voltage is zero (on left side)
45
Q

What happens when electrons pass through a wire?

A
  • collide with metal ions
  • ions get in way (resist flow)
46
Q

What happens to resistance if wire is longer?

A

the longer the wire, the greater the resistance

47
Q

What happens to resistance if wire is thick?

A

The thicker a wire, the smaller it’s resistance

48
Q

What is the relationship of proportionality of resistance and length?

A

Resistance is directly proportional to length

R is proportional to length

49
Q

What is the relationship of proportionality of resistance and cross - sectional area ?

A

Resistance is inversely proportional to the cross sectional area

R is proportional to 1/A

50
Q

What are the factors the amount of energy an appliances transfer deoends on?

A
  • how long the appliance is switched on for
  • the power of the appliance
51
Q

What is the formula used to calculate electrical energy?

A

E = VIt

E = energy ( joules, J )
V = voltage (volts,V)
I = current (amps,A)
t = time (seconds, s)

52
Q

What happens as electricity passes around a circuit?

A
  • charge passes through the power supply it is given energy
  • as it passes through a component, it loses energy
53
Q

What do most household appliances transfer energy from?

A

AC mainz

Kinetic energy of electric motor

54
Q

What are motors used in?

A
  1. Vacuum cleaners - to create suction to suck in dust and dirt off carpets
  2. Washing machines - to rotate drum or wash clothes
  3. Refrigerators - compress refrigerant chemical into liquid to reduce the temp
55
Q

What is heating used in?

A
  1. Toasters - to toast bread
  2. Kettles - to boil water
  3. Radiators - hot water is pumped from boiler so radiator can heat up room.
56
Q

Define power in terms of mechanics?

A

Rate of doing work

57
Q

What is power in mechanics?

A
  1. Potential difference = work done per unit time
  2. Current = rate of flow of charge
58
Q

Define electrical power.

A

Rate of change of work done

59
Q

What is the formula for power dissipated by an electrical device?

A

P = IV

P = power (W)
I = current (A)
V = potential difference / voltage (V)

60
Q

Substitute power equation with ohm’s law.

A

Resistance:
P = I^2 R

  • if current or voltage doubles, power will be 4 times as great.

Voltage:
P = V^2 / R

61
Q

What is the rearranged power and energy equation?

A

E = VIt

E = energy transferred (J)

V = potential difference (V)

I = current (A)
t = time (s)

62
Q

Define kilowatt hour.

A

A unit of energy equivalent to one kilowatt of power expended for one hour

63
Q

What do power rating on appliances tell consumers? kW h

A

The amount if energy transferred (by electrical work) to the device every sec

64
Q

What is the formula to calculate kilowatt hour?

A

E = Pt

E = Energy (kW h)
P = Power (kW)
t = time (h)

Physics - IGCSE (24 decks)

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