A Level Physics AQA > Electricity > Flashcards

Electricity Flashcards

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1
Q

Define electric current.

A

The flow of electric charge in a circuit

Electric current is measured in amperes (A) and is represented by the symbol I.

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2
Q

What is the formula for calculating charge flow (ΔQ) in a circuit?

A

ΔQ = IΔt

Where I is the current in amperes and Δt is the time in seconds.

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3
Q

What are charge carriers?

A
  • Electrons
  • Ions
  • Molecules

Charge carriers are particles that carry electric charge through a conductor.

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4
Q

What is the unit of current?

A

Ampere (A)

Defined in terms of the magnetic force between two parallel wires carrying the same current.

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5
Q

True or false: The direction of current is defined as the flow of positive charge from positive to negative.

A

TRUE

This convention was established before the discovery of electrons.

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6
Q

What happens to semiconductors when voltage is applied?

A

Electrons break free from atoms, allowing current to flow

The conductivity of semiconductors can be affected by temperature and impurities.

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7
Q

What is a rechargeable battery?

A

A battery that can be recharged and used multiple times

Examples include car batteries and batteries used in portable electronic devices.

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8
Q

Define potential difference.

A

The work done (or energy transferred) per unit charge

The unit of potential difference is the volt, which is equal to 1 joule per coulomb.

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9
Q

What is the unit of potential difference?

A

Volt

1 volt = 1 joule per coulomb.

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10
Q

The formula for potential difference (V) is given by _______.

A

V = W/Q

Where W is the work done and Q is the charge.

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11
Q

What does emf stand for?

A

Electromotive force

It is defined as the electrical energy produced per unit charge passing through the source.

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12
Q

The unit of emf is the same as the unit of _______.

A

Potential difference

Both are measured in volts.

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13
Q

Electrical power (P) is calculated using the formula _______.

A

P = IV

Where I is the current and V is the potential difference.

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14
Q

What is the unit of power?

A

Watt (W)

1 watt = 1 volt per ampere.

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15
Q

What happens to the resistor when energy is transferred through it?

A

It becomes hotter

This occurs because the charge carriers collide with atoms in the resistor.

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16
Q

What type of energy is transferred by a loudspeaker?

A

Sound energy

The electrical energy is converted into sound energy by the vibrating loudspeaker coil.

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17
Q

What is the definition of resistance in an electrical component?

A

The resistance is defined as the ratio of the pd across the component to the current through it

The unit of resistance is the ohm (Ω), which is equal to volts per ampere.

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18
Q

What is the equation for calculating resistance (R)?

A

R = V / I

Rearranging gives V = IR or I = V/R.

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19
Q

What is the unit of resistance?

A

Ohm (Ω)

1 ohm is equal to 1 volt per ampere.

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20
Q

What is the purpose of a resistor?

A

To have a certain resistance that remains constant regardless of the current

The resistance of a resistor can be measured using an ammeter and a voltmeter.

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21
Q

How should an ammeter be connected in a circuit to measure current through a resistor?

A

In series with the resistor

This ensures the same current passes through both the resistor and the ammeter.

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22
Q

How should a voltmeter be connected to measure the pd across a resistor?

A

In parallel with the resistor

This allows the voltmeter to measure the potential difference across the resistor.

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23
Q

What is Ohm’s Law?

A

The statement that the resistance of a conductor is constant under constant physical conditions

This law is named after Georg Simon Ohm, who formulated it in 1826.

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24
Q

What is a superconductor?

A

A material that exhibits zero electrical resistance below a certain temperature

Superconductors can conduct electricity without energy loss.

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25
What is **resistivity**?
A constant for a material that relates resistance to its dimensions ## Footnote The equation is R = ρ(L/A), where ρ is resistivity, L is length, and A is cross-sectional area.
26
What is the unit of **resistivity**?
Ohm metre (Ω·m) ## Footnote Resistivity is a property that varies with the material.
27
For a conductor with a circular cross-section of diameter d, what is the formula for **cross-sectional area (A)**?
A = π(r^2) where r = d/2 ## Footnote This formula is used to calculate the area for resistivity calculations.
28
What is the **definition of resistance** in an electrical component?
The resistance is defined as the ratio of the **pd across the component** to the **current through it** ## Footnote The unit of resistance is the **ohm (Ω)**, which is equal to volts per ampere.
29
What is the equation for calculating **resistance (R)**?
R = V / I ## Footnote Rearranging gives V = IR or I = V/R.
30
What is the **unit of resistance**?
Ohm (Ω) ## Footnote 1 ohm is equal to 1 volt per ampere.
31
What is the purpose of a **resistor**?
To have a certain resistance that remains constant regardless of the current ## Footnote The resistance of a resistor can be measured using an ammeter and a voltmeter.
32
How should an **ammeter** be connected in a circuit to measure current through a resistor?
In series with the resistor ## Footnote This ensures the same current passes through both the resistor and the ammeter.
33
How should a **voltmeter** be connected to measure the pd across a resistor?
In parallel with the resistor ## Footnote This allows the voltmeter to measure the potential difference across the resistor.
34
What is **Ohm's Law**?
The statement that the resistance of a conductor is constant under constant physical conditions ## Footnote This law is named after **Georg Simon Ohm**, who formulated it in 1826.
35
What is a **superconductor**?
A material that exhibits zero electrical resistance below a certain temperature ## Footnote Superconductors can conduct electricity without energy loss.
36
What is **resistivity**?
A constant for a material that relates resistance to its dimensions ## Footnote The equation is R = ρ(L/A), where ρ is resistivity, L is length, and A is cross-sectional area.
37
What is the unit of **resistivity**?
Ohm metre (Ω·m) ## Footnote Resistivity is a property that varies with the material.
38
For a conductor with a circular cross-section of diameter d, what is the formula for **cross-sectional area (A)**?
A = π(r^2) where r = d/2 ## Footnote This formula is used to calculate the area for resistivity calculations.
39
To determine the resistivity of a wire, you must measure the **________** of different lengths of wire.
resistance ## Footnote This is plotted against length to find the graph gradient.
40
What is a **superconductor**?
A material that has zero resistivity at and below a critical temperature ## Footnote Superconductors allow current to flow without any heating effect.
41
What happens to a superconductor when its temperature is raised above its **critical temperature**?
It loses its superconductivity ## Footnote The material will then exhibit resistance.
42
What are some applications of **superconductors**?
* High-power electromagnets * MRI scanners * Particle accelerators * Lightweight electric motors * Power cables without energy dissipation ## Footnote These applications benefit from the strong magnetic fields generated by superconductors.
43
Ammeter diagram
44
Voltmeter diagram
45
46
Cell diagram
47
Bulb diagram
48
Circuit diagrams of : Diode LED Resistor Variable resistor Thermistor Light dependent resistor Heater Electric motor
49
What is the function of a **cell** in a circuit?
A cell is a source of electrical energy ## Footnote A battery is a combination of cells.
50
What does a **diode** do?
Allows current to flow in one direction only ## Footnote A light-emitting diode (LED) emits light when it conducts.
51
What is the **forward direction** of a diode?
The direction in which the diode conducts ## Footnote The opposite direction is referred to as its reverse direction.
52
How does the resistance of a **thermistor** change with temperature?
Decreases with increasing temperature ## Footnote This applies if the thermistor is an intrinsic semiconductor such as silicon.
53
What happens to the resistance of a **light-dependent resistor (LDR)** with increasing light intensity?
Resistance decreases ## Footnote LDRs are used in applications where light levels need to be detected.
54
To measure the variation of current with **pd** for a component, which two methods can be used?
* A potential divider to vary the pd from zero * A variable resistor to vary the current to a minimum ## Footnote These methods help in investigating component characteristics.
55
Current vs PD for a wire
56
Current vs PD for a filament lamp (bulb)
57
Current vs PD for a Thermistor
58
Current vs PD for a diode
59
What happens to the **resistance** of a metal conductor as **temperature** increases?
Resistance increases ## Footnote This is due to the increased vibration of atoms in the conductor, making it harder for conduction electrons to pass through.
60
A metal has a **positive temperature coefficient** because its resistance ________ with an increase in temperature.
increases ## Footnote This means that as temperature rises, the resistance of the metal also rises.
61
What is the **current rule** for components in series?
The current entering a component is the same as the current leaving the component ## Footnote This means that the charge per second entering a component is equal to the charge per second leaving it.
62
In a series circuit, the current passing through two or more components is _______.
the same through each component ## Footnote The rate of flow of charge through each component is the same at any instant.
63
What does **potential difference** (pd) represent in a circuit?
The energy transfer per coulomb of charge that flows from one point to another ## Footnote If charge carriers lose energy, it is a potential drop; if they gain energy, it is a potential rise.
64
The formula for adding potential differences in a series circuit is _______.
Vo = V1 + V2 + V3 ## Footnote This indicates that the total potential difference is the sum of the potential differences across each component.
65
In a parallel circuit, the potential difference across components is _______.
the same ## Footnote Each coulomb of charge delivers the same amount of energy regardless of which resistor it passes through.
66
If the battery potential difference is 12V and the pd across a variable resistor is 4V, what is the pd across each of the two resistors in parallel?
8V ## Footnote Each coulomb of charge leaves the battery with 12J of electrical energy and uses 4J on passing through the variable resistor.
67
What is the significance of the **ammeter readings** in a series circuit?
They are the same because they measure the same current ## Footnote This reflects that the same amount of charge passes through each component.
68
What is the **loop rule** in electrical circuits?
The potential difference around the loop is equal to the sum of the potential drops around the loop ## Footnote This follows from the conservation of energy.
69
True or false: The internal resistance of a source of emf can usually be discounted.
TRUE ## Footnote This applies if the question states that the internal resistance is negligible.
70
In the context of a circuit, what does **emf** stand for?
Electromotive force ## Footnote It represents the energy provided by a source per coulomb of charge.
71
What is the formula for **total resistance** in resistors in series?
R = R1 + R2 + R3 + ... ## Footnote The total resistance is equal to the sum of the individual resistances.
72
In resistors in series, the **current** through each resistor is _______.
the same ## Footnote The same current passes through all resistors in series.
73
What is the relationship between **potential difference (pd)** and resistance in a series circuit?
V = IR ## Footnote The pd across each resistor can be calculated using Ohm's Law.
74
For resistors in parallel, the **potential difference (pd)** across each resistor is _______.
the same ## Footnote All resistors in parallel experience the same pd.
75
What is the formula for **total current** in resistors in parallel?
I = I1 + I2 + ... ## Footnote The total current is the sum of the individual currents through each resistor.
76
What is the formula for **current** through a resistor in parallel?
I = V/R ## Footnote The current through each resistor can be calculated using Ohm's Law.
77
In a parallel circuit, the **total resistance** can be calculated using the formula _______.
1/R_total = 1/R1 + 1/R2 + ... ## Footnote This formula is used to find the equivalent resistance of resistors in parallel.
78
What is the formula for **power (P)** supplied to a component?
P = IV = I²R = V²/R ## Footnote These equations show how power can be calculated using current, voltage, and resistance.
79
If a component heats up, its temperature rise depends on what two factors?
* Power supplied to it (IR) * Rate of heat transfer to the surroundings ## Footnote Understanding these factors is crucial for thermal management in electrical components.
80
What is the **internal resistance** of a battery?
The loss of potential difference per unit current in the source when current passes through the source ## Footnote Internal resistance is represented in circuit diagrams as a resistor in series with the cell or battery.
81
Why is the **pd of a battery** in use less than its emf?
Due to the internal resistance of the source ## Footnote The difference between the emf and the terminal pd is caused by the internal resistance.
82
What is the formula relating **emf**, **terminal pd**, and **internal resistance**?
E = IR + Ir ## Footnote Where E is the emf, I is the current, R is the external resistance, and r is the internal resistance.
83
What does the **lost pd** inside the cell represent?
The energy per coulomb dissipated or wasted inside the cell due to its internal resistance ## Footnote It is the difference between the cell emf and the pd across its terminals.
84
How can the **terminal pd** of a cell be measured?
By connecting a high-resistance voltmeter directly across the terminals of the cell ## Footnote The current can be changed by adjusting a variable resistor.
85
What type of graph is produced when plotting **terminal pd** against **current**?
A straight line with a negative gradient ## Footnote The gradient represents the internal resistance.
86
What does the **gradient** of the graph of terminal pd versus current represent?
The internal resistance ## Footnote The y-intercept of the graph represents the emf.
87
At any **junction** in a circuit, what is true about the total current?
The total current entering the junction is equal to the total current leaving the junction ## Footnote This is known as Kirchhoff's first law, or the current law.
88
For any complete **loop** in a circuit, what must be true about the sum of the emfs and potential drops?
The sum of the emfs around the loop is equal to the sum of the potential drops around the loop ## Footnote This is known as Kirchhoff's second law, or the voltage law.
89
What is a **potential divider**?
A circuit that divides the voltage into smaller parts ## Footnote It is used to supply a variable potential difference from a fixed source.
90
True or false: The ratio of the pds across each resistor in a potential divider is equal to the ratio of their resistances.
TRUE ## Footnote This principle is fundamental to understanding how potential dividers work.
91
What type of sensor can be used in a variable potential divider to measure temperature?
Thermistor ## Footnote The thermistor's resistance changes with temperature, affecting the output voltage.
92
In a light sensor, what happens to the resistance of an LDR (Light Dependent Resistor) when light intensity increases?
The resistance falls ## Footnote As the resistance decreases, the potential difference across the LDR also decreases.
93
Fill in the blank: A potential divider can supply a pd that varies with a physical condition such as _______.
temperature or pressure ## Footnote This allows for the creation of sensor circuits that respond to environmental changes.
94
What is the role of the sliding contact in a variable potential divider?
To adjust the output voltage ## Footnote Moving the contact changes the proportion of voltage across the resistors.
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