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A level physics > Electrical Circuits > Flashcards

Electrical Circuits Flashcards

1
Q

Switch

A

Opens / closes a circuit

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2
Q

Cell

A

Provides power to a circuit

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3
Q

Lamp / Bulb

A

Emits light by heating a filament

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4
Q

Resistor

A

Slows down the flow of electricity (current), providing resistance to a circuit

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5
Q

Variable resistor

A

Same as resistor, but the level of resistance can be changed

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6
Q

LDR

A

Changes resistance depending on the intensity of light. As the intensity increases, the resistance decreases

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7
Q

Thermistor

A

Changes resistance depending on temperature. As the temperature increases, resistance decreases.

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8
Q

Diode

A

Allows current to flow in one direction

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9
Q

LED

A

Light emitting diode
Converts electrical energy to light

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10
Q

Ammeter

A

Measures current

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11
Q

Voltmeter

A

Measures P.D

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12
Q

Fuse

A

Breaks a circuit when at a certain current

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13
Q

Energy

A

Capacity for doing work
Symbol: E
Unit: J, Joule
Equation: E = QV, E= Pt, E = FS
Base units: kgm^2 s-2

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14
Q

Frequency

A

Number of oscillations in a given time period (1s)
Symbol: f
Unit: Hertz, Hz
Equation: f = 1/T, f = v/λ
Base units: s^-1

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15
Q

Current

A

Rate of flow of electrical charge
Symbol: I
Unit: Amperes, A
Equation: I = Q/t, I = V/R, I = P/V
Base units: A

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16
Q

Potential difference

A

The energy supplied per coulomb of charge
Symbol: V
Unit: Volts, V
Equation: V = E/Q, V = IR
Base units: kgm^2 s^-3 A^-1

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17
Q

Power

A

Rate of energy transfer / work done
Symbol: P
Unit: Watts, W
Equation: P = E/t, P = IV, P = I^2R
Base units: kgm^2 s^-3

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18
Q

Charge

A

The physical property of matter that causes it to experience a force when placed in an electromagnetic field
Symbol: Q
Units: Coulombs, C
Equation: Q = It, Q = E/V
Base units: As

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19
Q

Resistance

A

The ratio of P.D across a component to current though it
Symbol: R
Unit: Ohms, Ω
Equation: R = V/I, R = P/I^2
Base units: kg ^2 s^-3 A^-2

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20
Q

Resistivity

A

Specific property of a material that measures its electrical resistance
Symbol: ρ
Units: Ohm meter, Ωm
Equations: ρ = RA/L (A = cross sectional area, L = length of wire)
Base units: kgm^4 s^-3 A^-2

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21
Q

Time period

A

Time take for one complete oscillation of a wave
Symbol: T
Unit: second, s
Equation: T = 1/f
Base units: s

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22
Q

Time

A

Measurable duration of an action, process, or condition
Symbol: t
Unit: second, s
Equation: t = E/P, t = Q/I
Base units: s

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23
Q

Ohm’s law

A

Voltage is directly proportional to current at a constant resistance.
V = R x I

24
Q

Kirchhoff’s first law

A

The total current into a junction equals the total current out a junction
I 1 = I 2 + I 3 + ……

25
Q

Kirchhoff’s second law

A

In any loop around a circuit, the sum of the EMFs equal the sum of the P.Ds

26
Q

Current in a series circuit

A

Current is constant in all parts
I 1 = I 2 = I 3

27
Q

Current in a parallel circuit

A

Current is split between branches based on resistance
I total = I 1 + I 2 + I 3

28
Q

Voltage in a series circuit

A

Shared amongst components
V total = V 1 + V 2 + V 3

29
Q

Voltage in a parallel circuit

A

Each loop gets the full voltage. The P.D is split between components in the loops
V total = V 1 = V 2 = V 3

30
Q

Resistance in a series circuit

A

Total resistance in the sum of the individual resistance of each component
R total = R 1 + R 2 + R 3

31
Q

Resistance in a parallel circuit

A

Reciprocal of total resistance in the sum of the reciprocals of the individual resistances
1/R T = 1/R 1 + 1/R 2 + …. 1/R n

32
Q

Typical trigger voltage for a diode

A

0.6V

33
Q

Forward bias

A

When a diode is setup in a way that allowed current to flow through

34
Q

Backward bias

A

When a diode is set up in a way that does not allow current to flow through

35
Q

Potential divider

A

A circuit with two or more resistors in series with each other. There is a source of fixed P.D between them, which is divided between the components in the circuit.

36
Q

Relationship between resistance of a component to the P.D over it in a potential divider

A

The proportion of resistance to the total resistance is equal to the proportion of the P.D to the total P.D over the component

37
Q

Potential divider equation

A

V1 = (V0 x R1) / (R1 + R2 + … Rn)

38
Q

What is the gradient of an IV graph?

A

1/R
Therefore, a steeper gradient is a lower resistance

39
Q

Three factors that influence resistance in a wire

A

Resistivity (directly proportional)
Length of the wire (directly proportional)
Cross sectional area (inversely proportional)

40
Q

Difference between Resistivity and resistance

A

Resistivity is a constant material property whereas resistance is sample specific, depending on length, cross sectional area, and Resistivity

41
Q

What is the magnitude of the charge per carrier unit?

A

1.6x10^-19

42
Q

What is the actual value of charge per carrier unit?

A

-1.6x10^-19

43
Q

Which direction do electrons move?

A

Negative to positive.

44
Q

What is drift velocity?

A

The average velocity that a particle attains due to an electric field.

45
Q

Describe the motion of electrons in an ionic lattice with no P.D

A

Moving about in random directions. No net velocity.

46
Q

Describe the motion of electrons with a P.D

A

Moving about in random directions, however with a mean velocity. Net velocity isn’t 0.

47
Q

Describe the atomic structure of a wire.

A

Ions surrounded by de localised electrons

48
Q

Drift velocity equation

A

I = nAve where;
- I = current, A
- n = number density if metal, m^-3
- A = cross sectional area, m^2
- v = drift velocity, ms^-1
- e = electron charge, coulombs

49
Q

What is internal resistance?

A

The resistance within the cell

50
Q

When is the terminal P.D equal to its emf?

A

Only when no current is drawn, since Vlost = I x r internal

51
Q

Equation for total current with emf, R and r

A

I total = emf / (R+ r)

52
Q

Equation for emf with vlost and vload

A

Emf = Vload + vlost
Or
Emf = I total R + I total r

53
Q

4 physical properties that influence current in a wire

A

Cross sectional area
Drift velocity
Number density of metal
Charge carried per electron

54
Q

Energy transfers in a wire with resistance

A

Electrical energy -> work done -> thermal energy

55
Q

How do thermistors work?

A

With more temperature, electrons are pushed into the conduction band form the valence band due to having more energy.
The electrons are excited and are no longer part of the atom.
Hence, more electrons are available to carry charge, so resistance decrease. (Number density increases)

56
Q

How do LDRs work?

A

Whenever light falls on the photoelectric material, it absorbs energy causing electrons in the valence band to be excited into the conduction band. More electrons available to carry charge = lower resistance.

A level physics (5 decks)

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