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Alevel Physics (Edexcel) > Topic 3 > Flashcards

Topic 3 Flashcards

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1
Q

Define electrical current

A

Electrical current is the rate of flow of charge

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2
Q

State the defining equation for current

A

I = ΔQ / Δt

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3
Q

What is the unit of current

A

Ampere (Amps), A

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4
Q

Define voltage

A

Voltage is the work done per unit charge

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5
Q

State the defining equation for voltage

A

V = W / Q

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6
Q

What equation links current, voltage and resistance?

A

Voltage (V) = Current (A) x Resistance (Ω)

V=IR

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7
Q

What is ohm’s law?

A

If Ohm’s law is obeyed, the current and voltage passing through a component are directly proportional, when at a constant temperature

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8
Q

Describe the distribution of current in a series circuit

A

In a series circuit, the current is the same at all positions in the circuit

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9
Q

What law is the distribution of current in a series circuit a consequence of?

A

The law of the conservation of charge. Charge cannot be created or destroyed and so in a closed loop, the flow of charge must be the same throughout

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10
Q

Describe the distribution of current in a parallel circuit

A

In a parallel circuit, the current is split between the different branches. The current entering each branch must be the same as the current leaving it

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11
Q

Explain how the conservation of charges applies to parallel cicuits

A

Charge cannot be created or destroyed meaning the total current leaving the source must equal the sum of the currents in all the individual branches

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12
Q

What law is the distribution of potential differences in a circuit a consequence of?

A

The law of the conservation of energy

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13
Q

Describe the distribution of potential differences in a series circuit

A

The total potential difference is split across all the components in a series circuit, in the ratio of their resistances.

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14
Q

Describe the distribution of potential differences in a parallel cicuit

A

The sum of the potential differences in each branch of a parallel circuit, is the same and will be equal to the potential difference of the source

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15
Q

What equation relates power, current and potential difference?

A

P=IV

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16
Q

How can you calculate the work done over a given time period, by a component with a known potential difference and current?

A

Combining P = W/t and P=IV gives:

W=IVt

17
Q

What is the IV characteristic for an ohmic conductor?

A

Directly proportional

18
Q

Explain the IV characteristic for a filament bulb

A

The higher the current, the higher the temperature of the metal filament
The higher the temperature, the higher the KE of the metal ions and so the more they vibrate
This makes it harder for current to flow and so the resistance of the bulb increases

19
Q

What three physical factors affect the resistance of a wire?

A

Length
Cross-Sectional Area
Resistivity

20
Q

How does increasing the length of a conductor affect its resistance?

A

The longer the conductor is, the higher its resistance, assuming all other factors remain the same

21
Q

How does increasing the cross-sectional area of a conductor affect its resistance?

A

The larger the cross-sectional area of a conductor, the lower its resistance, assuming all other factors remain the same

22
Q

What is resistivity?

A

A characteristic property of a material that determines its resistance to current flow

23
Q

Compare the resistance of two conductors of the same dimensions, but with different resistivities

A

The conductor with the higher resistivity will have the higher resistance

24
Q

State the equation linking the factors affecting the resistance of a conductor

A

R = ρL / A

25
Q

What equation links the number of charge carriers in a metal, along with their drift velocity, to the current flow?

A

I = nqAv

26
Q

How does the potential along a uniform current-carrying wire vary as you move along it?

A

The potential will increase as you move along the wire

27
Q

What is the electromotive force of a power supply?

A

The electromotive force is the amount of energy that is transferred to each Coulomb of charge that passes through it

28
Q

What is the terminal potential difference of a power supply?

A

The terminal potential difference of a power supply is the actual potential difference that is produced across the terminals of the supply and is provided to the circuit

29
Q

Why does the electromotive force of a supply differ from its terminal potential difference?

A

Some of the energy that is transferred to the charges is used to overcome the internal resistance of the power supply

30
Q

Define internal resistance

A

The internal resistance of a power supply is the electrical resistance, when a current flows, due to the materials within the supply itself

31
Q

Describe a method to determine the terminal potential difference of a battery

A

Attach a voltmeter directly across the terminals of the battery when it is isolated. Since no current flows, no potential is lost due to internal resistance and so the voltmeter will read the value of the terminal p.d.

32
Q

What is a semiconductor?

A

A semiconductor is a component that can change its resistance based on external conditions

33
Q

Give two examples of semiconductors and state what they are sensitive to

A

Thermistors are sensitive to temperature

LDRS are sensitive to light

34
Q

Describe how the resistance of a thermistor changes as temperature decreases

A

As temperature decreases, the resistance of a thermistor will increase

35
Q

Explain why the resistance of a thermistor will decrease with an increase of temperature

A

As temperature increases, conduction electrons are liberated, meaning there are more charge carriers and so current can flow more easily

36
Q

Describe how the resistance of an LDR changes as light intensity increases

A

As light intensity increases, the resistance of an LDR will decrease

37
Q

What is a potential divider?

A

A potential divider is a pair of resistors used to split the potential difference over them into a given ratio

38
Q

What is the link between the resistances and the potential differences in a potential divider?

A

The potential difference of the circuit is split in the ratio of the resistances of the resistors

Alevel Physics (Edexcel) (13 decks)

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