Electricity Flashcards

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1
Q

What is electric current?
What is it units?

A

The rate of flow of charge. Measured in amperes

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2
Q

What is potential difference?

A

The work done per unit charge between 2 points in a circuit

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3
Q

What is resistance?

A

Opposition to current, for a given potential difference.
How difficult it is for current to flow through a circuit

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4
Q

What is meant by an ohmic conductor

A

A conductor which obeys ohm law
Meaning that current is directly proportional to potential difference provided the physical conditions remain constant (temperature).

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5
Q

Draw the iv graph for an ohmic conductor.
Explain it

A
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6
Q

Draw the iv graph for a filament bulb
Explain it.

A

Due to increasing resistance from higher temperatures causing metal ions to vibrate more, causing a greater number to collide with the flow of electrons

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7
Q

Why does the current increasing on a a filament lamp cause an increase in resistance

A

As current flows through the lamp
Electrical energy is converted to heat energy
Metal ions therefore vibrate with increased amplitudes
Which impedes the movement of electrons through the lamp as they have a higher chance of collision with these metal ions, showing an increase in resistance

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8
Q

What is a diode

A

An electrical appliance that only allows current in a specific direction

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9
Q

Draw the IV graph of a diode

A
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10
Q

Why are voltmeters assumed to have infinite resistance

A

Current takes the path of least resistance
When applied in parallel to the original circuit no current will flow through the voltmeters branch
So conditions are exactly the same before the addition of the voltmeter

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11
Q

Why must you assume the ammeter has zero resistance

A

So no power or potential difference is disapated in the ammeter

So that conditions for the rest of the components are exactly the same as before

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12
Q

What is a LDR?

A

A semi conductor that varies its resistance depending on the intensity of light incident

As light intensity increases its resistance decrease

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13
Q

How does a thermistor work

What is the difference between a NCR and a PCR resistors

A

A semi conductor that is sensitive to temperature

NCR’s resistance decreases as temperature increases
PCR’s resistance increases as temperature increases

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14
Q

What is resistivity

A

Resistance of a conductor of a cross sectional area per unit length.

The resistance of a 1m cylinder with a cross sectional area of 1M^2

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15
Q

Describe an experiment to determine the resistivity of a material

A

1) Measure the diameter of the wire with a vernier calliper at multiple places along the wire and take an average
2) Set up the circuit shown
3) Vary the wire length and record the voltage and current for each length
4) Use R = V/I to work out the resistance
5)Plot a graph of resistance against wire length
6) Gradient = Resistivity/ Cross sectional area
7)Resistivity = Gradient * cross sectional area

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16
Q

What is a superconductor

A

A material that has a resistivity of zero at or below a critical temperature

17
Q

How do you find the total resistance of a series circuit

A

R1+R2+R3…… = RT

18
Q

If 6 cells have a voltage of 5v, arranged in parallel
What is the voltage in the circuit

A

5 volts

19
Q

How does the current vary between each component in a series circuit

A

The current through all of the components is the same

20
Q

What is Kirchoffs first law

A

The sum of the currents entering a junction is the same as the sum of the currents exiting a junction

So charge is conserved

21
Q

What is Kirchoffs 2nd law

A

The sum of the EMF’s in a closed loop is equal to the sum of the potential differences.

So energy is conserved

22
Q

What is power?

A

The rate of which work is done.

23
Q

What is the purpose of a potential divider

A

To provide a constant specific potential difference to an external circuit

24
Q

What is the equation for a potential divider?

A

Where R2 is the resistor that you want to measure the resistance of.

25
Q

What is emf?

A

Electromotive force

The energy transferred from other forms to electrical potential per unit charge

26
Q
A

V = -1 * internal resistance * current + emf

27
Q

The temperature is increased in the following circuit

Explain what happens to the output potential difference

A

Resistance of thermistor decreases

Output PD decreases, as the resistance of the parallel combination decreases.

Resulting in a less proportion of the potential difference across it.

28
Q

Explain why the reading on the voltmeter decreases as the brightness of the lamp increases

A

For the brightness of the lamp to increase, currents must increase

Higher current means that the variable resistor decreases in resistance

This means that the ratio of internal to external resistance increases

A higher proportion of emf is dissipated in the internal resistance of the cell / increase in lost volts

So PD across external circuit decreases

29
Q

Explain the effect on the brightness of the lamp if another cell is connected in parallel to the other cell

A

Emf of circuit is identical

Parallel combination of the Cells Internal resistances means a lower total internal resistance

Effective internal resistance is a smaller proportion of the total resistance.

Higher proportion of the potential difference is dissipated across the external circuit.