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Electricity Flashcards

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1
Q

Define Potential Difference, Voltage, Current and Resistance.

A

P.D - Work done per unit of charge over a section of the circuit.
Voltage - Work done per unit of charge.
Current - Rate of flow of charge.
Resistance - The difficulty of how current can flow in a given material or component.

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2
Q

How do you calculate voltage, current and resistance?

A 
Voltage = Current x Resistance
Voltage = Work done / Charge
Current = Voltage / Resistance
Current = Charge / time
Resistance = Voltage / Current
Resistance = Resistivity x Length / Area
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3
Q

What is meant by the term lost volts?

A

The lost volts is the voltage used by the battery or cell’s internal resistor.

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4
Q

How can you calculate the EMF of a circuit?

A

Measure the voltage across the battery or cell when the circuit is open y using a switch.

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5
Q

How can you calculate the EMF of a circuit?

A 
EMF = I(r + R)
EMF = lost volts + terminal p.d
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6
Q

How can you calculate the internal resistance of a circuit if you know the EMF?

A 
r = (EMF / current) - Resistance
r = (EMF - terminal p.d) / Current
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7
Q

What does a graph of terminal p.d against current tell us?

A

Y-intercept is the circuit’s emf

Gradient is the internal resistance of the circuit

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8
Q

How do you find the total resistance of 2 resistors in series with each other?

A

Add the resistances together.

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9
Q

How do you find the resistance of 2 resistors in parallel with each other?

A

Add their reciprocals together and then divide 1 by the answer.

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10
Q

What are Kirchhoff’s circuit laws?

A
  1. Total current entering a circuit is the total current leaving the circuit
  2. In any closed loop network, the total voltage around the loop is equal to the sum of all the voltage drops within the same loop
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11
Q

What is a potential divider?

A

A potential divider consists of 2 or more resistors in series with a fixed source of potential difference.

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12
Q

What are the uses of Potential Dividers?

A

To supply a fixed supply of voltage between 0 and the source P.d.
To supply a variable P.d.
To apply a P.d that varies with environmental conditions, such as temperature or pressure.

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13
Q

What happens to the current in a circuit when it is in series?

A

Current remains constant in a series circuit.

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14
Q

What happens to the current when the circuit is in parallel?

A

The current is split down each path according to the ratio between the branches total resistance.

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15
Q

What happens to the P.d across the parallel branches?

A

The P.d across each branch is the same as the source p.d.

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16
Q

What is the resistance of a diode?

A

A diode will have infinite resistance in the opposite direction, not allowing current to pass through it.

17
Q

What is the relationship between Current and Voltage of a filament when the temperature is constant?

A

They are directly proportional with their graph being a straight line through the origin and positive and negative quadrants.

18
Q

What does the Voltage and Current graph of a filament lamp look like when temperature isn’t constant?

A

The graph will start off directly proportional but as the temperature rises, the resistance in the circuit will increase as more energy will be transferred to the fixed metal ions causing them to vibrate more. This causes the voltage to increase at a lower rate.

19
Q

What does a diode’s voltage - current graph look like?

A

The graph will have almost not current at very low voltages and negative voltages, but will have a big spike in current over a small increase in voltage and will then increase much steadier.

20
Q

How does a thermistor’s resistance vary with its temperature?

A

At low temperatures, the thermistor will have a high resistance and at high temperatures, the thermistor will have a low resistance.

21
Q

What is the total voltage of a circuit when it has 2 cells in series?

A

The total voltage is each of the cell’s voltages added together.

22
Q

What is the total voltage of a circuit when it has 2 cells in parallel with each other?

A

The total voltage is equal to the voltage the voltage will be a balance between them both, half of their total.

23
Q

What are the power equations that link voltage, current and resistance.

A 
Power = Current x Voltage
Power = Current^2 * Resistance
Power = Voltage^2 / Resistance
24
Q

What is a superconductor?

A

A superconductor is a material or component that has no resistance. This is achieved by cooling down the object to extremely cold values - close to absolute zero (0K or -273 C)

25
Q

What are some uses of superconductors?

A

Superconductors can be used in MRI scans and in trains that use magnets to float off the tracks

26
Q

Define voltage, potential different, current and resistance.

A

Physics (7 decks)

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