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Physics > 5: Electricity > Flashcards

5: Electricity Flashcards

1
Q

What is terminal p.d?

A

The voltage directly across a power supply (with internal resistance)

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2
Q

What are the equations for emf?

A

emf=current multiplied by the total resistance
(ε=I(R+r))
emf=energy supplied/charge

Where:
ε=emf
I=current
R=circuit resistance
r=internal resistance

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3
Q

What are two applications of superconductors?

A

-Used in power cables to reduce energy loss via heating to zero
-Used in strong magnets

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4
Q

What is the emf?

A

-The electrical energy transferred by a power supply per unit charge
-The work done required to push a charge around a circuit

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5
Q

What is Kirchhoff’s first law?

A

-The current into a junction must equal the current leaving that junction

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6
Q

What is Kirchhoff’s second law?

A

-The sum of all voltages in a loop equals zero

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7
Q

What is a superconductor?

A

-A material which has zero resistance at or below a critical temperature

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8
Q

How does resistance change for a Light Dependent Resistor?

A

-As light intensity increase the resistance decreases

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9
Q

What is a potential divider?

A

-A circuit that turns a changing resistance into a change potential difference

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10
Q

How is charge conserved in a circuit?

A

-The current is equal at each point in a series circuit

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11
Q

How is energy conserved in a circuit?

A

-Total voltage input equals the sum of voltages across components

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12
Q

How do voltages sum when cells are connected in series?

A

-The voltages add together

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13
Q

How do voltages sum when cells are connected in parallel?

A

-The overall voltage remains the same

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14
Q

How do currents sum when cells are connected in series?

A

-There is no change in overall current

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15
Q

How do currents sum when cells are connected in parallel?

A

-The current will increase as the total resistance decreases

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16
Q

How do resistances sum when cells are connected in series?

A

-The resistances add together

17
Q

How do resistances sum when cells are connected in parallel?

A

-Combining cells in parallel will decrease the overall resistance

18
Q

Why does increasing current increase resistance for a filament lamp?

A

-As current flows electrical energy is converted to thermal energy
-This causes the metal ions to vibrate more
-Which in turn further impedes the movement of electrons thus making it harder of current to flow

19
Q

How would you determine the resistivity of a metal (experiment)?

A

-Measure the diameter with a micrometer in several places and calculate a mean
-Calculate the cross-sectional area by π*(d^2)/4
-Vary the wire length and record voltage with a voltmeter and current with an ammeter
-Repeat this for multiple lengths of wire and calculate the resistance for each length
-Repeat the experiment twice more to calculate mean resistances
-Plot a graph of resistance against length
-The resistivity is the gradient multiplied by the area

20
Q

What are the power equations?

A

P=V.I
P=(V^2)/R
P=(I^2)*R

W=P.T

Where:
W=work done
P=power
V=voltage
I=current
R=resistance

21
Q

How do resistors sum in a series cirucit?

A

-RT=R1+R2…

22
Q

How do resistors sum in a parallel circuit?

A

-1/RT=1/R1+1/R2…

23
Q

How does resistance change for a thermistor?

A

-As temperature increase the resistance decreases

24
Q

How are thermistors used in temperature sensors?

A

-As temperature of thermistor increases the resistance will decrease
-This will decrease the total resistance and increase the current
-This will increase the voltage across the fixed resistor and decrease the voltage across the thermistor
-This allows you to measure a voltage for the thermistor and when the voltage is too low you will know the temperature is too high

25
Q

How do you calculate resistivity?

A

-Resistivity equals (Resistance*Area)/Length

26
Q

How much resistance does an ideal voltmeter have?

A

-Infinite resistance

27
Q

How much resistance does an ideal ammeter have?

A

-Zero resistance

28
Q

What is ohm’s law

A

-For a constant temperature the current is directly proportional to the potential difference

29
Q

What is resistance?

A

-A measure of how difficult it is for current to flow through a component
-R=V/I
Where:
V=voltage
I=current
R=resistance
-Measure in ohms

30
Q

What is potential difference?

A

-The work done per unit charge
-V=W/Q
Where:
V=voltage
W=work done
Q=charge
-Measure in volts

31
Q

What is current?

A

-The rate of flow of charge
-I=ΔQ/Δt
Where:
I=current
Q=charge
t=time
-Measured in amps

32
Q

Information that can’t be put on flashcards

A

-Graph for filament lamp
-Graph for semiconductor diode
-Graph for Ohmic conductor
-Circuits

Physics (11 decks)

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