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A Level Physics > Electricity > Flashcards

Electricity Flashcards

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1
Q

Define Current.

A

Current is the flow of electrons within a wire. The rate of flow of charged particles measured in ampere (A).

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2
Q

Define Potential Difference

A

P.D. is the energy transferred per unit charge when the charge moves between 2 points across a component.

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3
Q

Define Power.

A

Power is the rate of transfer of energy.

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4
Q

Define resistance.

A

Resistance is the ratio of the p.d. across a component to the current through it.

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5
Q

What is the equation for resistance?

A

R=V/I

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6
Q

What is the equation for current in terms of R, V and I?

A

I=V/R

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7
Q

What is the equation for P.D.?

A

V=IR

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8
Q

What is Kirchhoff’ 1st Law?

A

About the current and the conservation of charge. The amount of current going into a junction must be the same as laving it, I1 + I2 = I3.

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9
Q

What is Kirchhoff’ 2nd Law?

A

The sum of the emfs is equal to the sum of the p.d.s around any closed loop in circuit.

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10
Q

What is an ohmic resistor?

A

A resistor that obeys Ohms law, for a conductor (metals or ohmic conductor) at a constant temperature the current is directly proportional to the potential difference across it.

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11
Q

What shape is the line or curve for the ohmic conductor graph?

A

A straight, linear line.

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12
Q

What shape is the line or curve for the filament bulb graph?

A

A S shape.

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13
Q

What shape is the line or curve for the silicone diode graph?

A

A flat line into a suddenly increasing steep gradient at 0.6V onwards.

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14
Q

Define resistivity.

A

Resistivity is the resistance (that opposes the rate of electric current through it) of a cubic metre of a substance varying from metal to metal and does increase as the temperature goes up.

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15
Q

What is a superconductor?

A

A superconductor is a substance capable of becoming superconducting at sufficiently low temperatures.

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16
Q

What are superconductors used for?

A

Superconductors are also used to power railguns and coilguns, cell phone base stations, fast digital circuits and particle detectors. Essentially, anytime you need a really strong magnetic field or electric current and don’t want your equipment to melt the moment you turn it on, you need a superconductor.

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17
Q

Why does the resistance of a filament lamp depend on the currency flowing through it?

A

The higher the current the hotter the filament lamp gets. As the temperature increases, the metallic lattice vibrates more and the electrons collide with the positive ions more frequently when trying to get through, therefore increasing the resistance.

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18
Q

Why does light intensity affect the resistance of a light dependent resistor?

A

The resistance of an LDR changes with the amount of light that falls on it. The light energy produces more free electrons which increases the current for a certain voltage across the LDR which means a drop in resistance. Higher the light intensity, the lower the resistance.

19
Q

Why does temperature affect the resistance of a thermistor?

A

At constant temperature its resistance is constant, the resistance only decreases as its temperature increases. This is because it is a semiconductor, and more free electrons are released when it gets hotter, meaning more charge carriers are able to carry current.

20
Q

Where should an ammeter be placed in a circuit?

A

In series

21
Q

Where should a voltmeter be placed in a circuit?

A

In parallel

22
Q

Which way does a current flow? What about electrons?

A

Convention current moves from positive to negative.
Electrons move the opposite direction, from negative to positive.

23
Q

What is a Coulomb?

A

Unit for charge. 1 coulomb is the charge that flows past a point in one second when there is a current of 1A (amp).

24
Q

Formula for charge?

A

Q=It
Charge = Current x time

25
Q

Formula for charge to do with e, N, Q?

A

Q=Ne
Charge = Number of electrons x charge on one electron

26
Q

What is emf?

A

Electromagnetic force (is not a force) is the amount of energy transferred from chemical energy to electrical energy per unit charge.

27
Q

What is the difference between emf and p.d.?

A

emf = per unit charge of chemical to electrical
p.d. = electrical to other forms (why the voltmeter is placed around the component)

28
Q

Formula for p.d. including work done and charge?

A

V=W/Q
p.d. = Energy/charge

29
Q

What is the current in series of the circuit?

A

Same for all components

30
Q

What is the current in parallel of the circuit?

A

Split and shared between branches

31
Q

What is a Volt?

A

The p.d. between 2 points when 1J of work is done to move a charge of 1C.

V = W/Q

32
Q

What is Ohms law?

A

Provided the physical conditions, such as temperature, are constant, the current through an ohmic conductor is directly proportional to the p.d. across it.

33
Q

Formula for power?

A

P=W/t
Power = Work done/time

34
Q

Formula for current with I, Q and t?

A

I=Q/t
Current = Charge/time

35
Q

Formula for electrical energy in terms of Q and V?

A

W=QV
Electrical energy = Charge x p.d.

36
Q

Formula for electrical energy in terms of t, I and V?

A

W=ItV
Electrical energy = Current x Time x p.d.

37
Q

Formula for power in terms of V and I?

A

P=IV
Power = Current x p.d.

38
Q

What is 1 ohm?

A

It is the resistance of a component that has a p.d. across it of 1V per ampere of current in it.

39
Q

Formula for resisitivity?

A

(Resistance x area) / length

40
Q

The explanations of the I-V graph for the filament bulb?

A

If the current passes a certain point it starts to heat up, more current = hotter.
Resistance increases because temperature increases which means the metallic lattice vibrates more and the electrons collide with the positive ions more frequently when trying to get through.
Current increases at a smaller amount than the p.d. across it.

41
Q

The explanations of the I-V graph for the Silicon diode?

A

Only conducts though one direction (forward biased).
Only conducts if the p.d. across it is at least 0.6V.
Over that 0.6V the current through this component increases by a much greater proportion than the p.d. across it.
A protective resistance should be laced before the diode in series in order to stop a large current flowing through and damaging the circuit, as there is little to none resistance through the diode (when forward biased).

42
Q

The explanations of the I-V graph for the Thermistor/Ohmic conductor?

A

Constant temp = constant resistance.
This component’s resistance decreases as its temperature increases.
It is a semiconductor, and more free electrons and release when it gets hotter, meaning more charge carriers are able to carry energy/charge.

43
Q

Two resistors R1 and R2 are made of wires of the same material. The wire used for R1 has half
the diameter and is twice as long as the wire used for R2.

What is the value of the ratio of R1/R2?

A

8

A Level Physics (15 decks)

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