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Physics > 3.5 Electricity > Flashcards

3.5 Electricity Flashcards

1
Q

What is electric current?

A

The rate of flow of charge.

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2
Q

What is potential difference?

A

Work done per unit charge.

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3
Q

What is resistance?

A

Potential difference/ current

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4
Q

What is ohms law?

A

At constant temperature, the current through an ohmic conductor (e.g. metals) is directly proportional to the voltage. (It’s a special case)

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5
Q

What are the ideal properties of ammeters?

A

They have zero resistance.

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6
Q

What are the ideal properties of voltmeters?

A

They have infinite resistance.

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7
Q

What is the equation for resistivity?

A

(Resistance)*(area) / (length)

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8
Q

What is the the qualitative effect of temperature on the resistance of thermistors?

A

They have a negative temperature coefficient. So, when temperature goes up, resistance decreases. When temperature increases, charge carriers are released as they have enough energy to leave their atom.

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9
Q

What is the qualitative effect of temperature on the resistance of metal conductors?

A

It has a positive temperature coefficient. So, when temperature increases, resistance increases.

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10
Q

What are the uses of thermistors?

A

Temperature sensors
Resistance-temperature graphs

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11
Q

What is superconductivity?

A

A property of certain materials which have zero resistivity at and below a critical temperature, which depends on the material.

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12
Q

What are the applications of superconductors and why?

A

Power cables that transmit electricity without any loss of power.
Really strong electromagnets that don’t need a constant power source (for use in MRI scanners and Maglev trains).
Electronic circuits that work really fast, because there’s no resistance to slow them down.

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13
Q

What is electromotive force?

A

The amount of electrical energy the battery produces for each coulomb of charge.

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14
Q

How do you calculate the total e.m.f for cells in series?

A

Add the individual e.m.fs together.

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15
Q

What is the total e.m.f for identical cells in parallel?

A

It’s the same as the emf of one cell.

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16
Q

What is the conservation of charge in circuits? (Kirchhoff’s 1st law)

A

The sum of current entering a junction is equal to the sum of current leaving it.

17
Q

What is the conservation of energy in circuits? (Kirchhoffs 2nd law)

A

The total e.m.f. around a series circuit = the sum of the p.d.s across each component.

18
Q

What are potential dividers used for?

A

To split the potential difference. To provide variable pd.

19
Q

What are some examples of potential dividers?

A

Variable resistors
Thermistors
Light dependent resistors (LDR)

20
Q

What is the qualitative effect of light on the resistance of an LDR?

A

A light-dependent resistor (LDR) has a very high resistance in the dark, but a lower resistance in the light.

21
Q

What is internal resistance?

A

I(R+r) . Some electrical energy is used up in the source as heat energy which is why batteries get hot when in a complete circuit.

22
Q

What is terminal pd?

A

Voltage which is measured across the cell.

23
Q

What 3 factors determine resistance?

A

Length- The longer the wire, the more difficult it is to make a current flow.
Area- The wider the wire, the easier it will be for the electrons to pass along it.
Resistivity- which depends on the material. The structure may make it easy or difficult for charge to flow. Resistivity depends on environmental factors as well, like temperature and light intensity.

24
Q

What is the definition of resistivity?

A

The resistance of a 1m length with a 1m^2 cross-sectional area.

25
Q

What is a potential divider?

A

A combination of resistors in series connected to a voltage source, which split the pd.

26
Q

Describe the procedure to investigate the EMF and internal resistance of a power supply.

A

Read ammeter and voltmeter
adjust resistance of variable resistor
and repeat (readings)
plot V (against) I
EMF = (vertical / y-axis) intercept
r=-gradient

Physics (7 decks)

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