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Higher Physics > Electricity > Flashcards

Electricity Flashcards

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1
Q

Terminal Potential Difference

A

Potential difference that appears across the terminals of a source
It is this potential difference that appears acrossthe external resistance

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2
Q

Lost Volts

A

The difference between emf and the tpd
The potential difference used to drive a current through the internal difference of a source
Given by Ir

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3
Q

Electromotive Force

A

The energy given by the source to each one of the charges passing through the source
Is equal to the sum of all the potential differences across all resistors
Including Pd across internal resistance r

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4
Q

What is the DC equivalent of 2.0v rms?

A

2.0v

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5
Q

The TPD is always

A

Less than the emf of the source

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6
Q

Ideal supply

A

Has no internal resistance

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7
Q

Short circuit

A

Has zero or little resistance

Current flows through a short rather than the component, removing it from the circuit.

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8
Q

Open circuit

A

Has infinite or high resistance
Gap in the circuit
No current flows

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9
Q

Capacitance of a capacitor found by

A

The slope of the line of a charge against potential difference graph

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10
Q

Energy stored in a capacitor given by

A

Area under a charge against potential difference graph

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11
Q

Emf= (Due to conservation of energy)

Vlost=

A

Vtpd + vlost

Ir

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12
Q

Emf on a graph

A

Y-Intercept (Terminal Pd) axis

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13
Q

Internal Resistance on a graph

A

Slope of the line = -r

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14
Q

Factors determining time for capacitor to charge

A

Resistance of a circuit - higher limits current and takes longer for capacitor to charge
Capacitance - Higher means that it will take longer to charge as it can hold more coulombs of charge per volt - charge takes longer to fill capacitor

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15
Q

Ohm’s Law (V=IR)

A

The potential difference across a component is proportional to the current flowing through it

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16
Q

Why Terminal potential difference falls when source current increases

A

Number of lost volts also increases
As lost volts is equal to the current multiplied by (the constant) internal resistance
A larger current causes more lost volts
Lost volts are not available at the terminals and so terminal pd falls

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17
Q

Why car batteries have a very low internal internal resistance

A

Cells which deliver a high current have a higher number of lost volts which means lower tpd
These Cells must have a very low internal resistance in order to deliver enough current to start the starter motor

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18
Q

Short circuit current formula

Derived from E=I(R+r)

A

Ishort= E/r

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19
Q

Wheatstone bridge circuit

A

When two potential dividers are connected in parallel

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20
Q

Frequency of an AC supply

Using the period

A

Number of boxes across the way for a cycle X Time Base setting gives period - T
Use f=1/T

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21
Q

Peak voltage of an AC supply

Using peak to calculate rms voltage

A

Height of trace above middle X voltage gain

Use formula Vrms= VPeak /sqrt2

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22
Q

1F is equivalent to

A

1cv^-1

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23
Q

State an application of capacitors

A

Flashing indicators

24
Q

Reducing the value of a capacitor/resistor (For an application of capacitors) will

A

Allow a capacitor to charge in less time
The lamp will flash more frequently
Time between each flash will be less
As capacitance is less the capacitor discharges in less time and so the light is lit for less time
AND the capacitor will store less energy so the flash will be less bright

25
Q

Metals are

A

Good conductors

Highest occupied band is not completely full - Conduction Band

26
Q

In an insulator

A

Highest occupied band is full
First unfilled band is conduction band
Large gap between valence and conduction band
Not enough energy for electrons to move from valence to conduction band

27
Q

In a semiconductor

A

Gap between valence and conduction band is smaller

At room temp there may be enough energy to move some electrons from valence to conduction band

28
Q

An increase in temp in a semi conductor

A

Increases the conductivity of the semi conductor

29
Q

An electron is a (Pn junctions)

A

Negative charged carrier

30
Q

A hole is a

A

Positive charged carrier

A position where an electron is missing

31
Q

n-type semiconductor

A

Material which has an excess of free electrons
Is made by doping with atoms having 5 electrons in their outer shell
They have more electrons than a pure semiconductor of the same size

32
Q

p-type semi-conductor

A

Material which has an excess of free holes
Majority charge carriers are positive holes
They have fewer electrons than a pure semi-conductor of the same size

33
Q

All n-type and p-type conductors are

A

Electrically neutral

34
Q

Hole movement really is

A

The movement of electrons filling holes and leaving new ones in the atom they came from

35
Q

Doping has the effect of

A

Lowering the resistance of the semiconductor

36
Q

Depletion Layer

A

The area surrounding the p-n junction of a diode
Electrons have combined with holes
No excess charges

37
Q

As bias voltage is increased

A

Current through the diode will also increase
Current IS NOT directly proportional to the voltage
Diodes referred to as ‘non-ohmic’ conductors

38
Q

When supply voltage is greater than depletion layer voltage - Forward Bias only

A

Free electrons in n-type conduction band can be pushed across the depletion layer
Up into conduction band of p-type semi-conductor

39
Q

Leakage current

A

The tiny amount of current in a reverse-biased diode

40
Q

Reverse Bias

A

Acts as a very high value resistor
When p type material is connected to the negative of the supply
Electrons at that side have more potential energy than under no bias
Raises bands on p-type side
Increases slope of depletion layer and is harder for electrons to cross that barrier
No current as no conduction

41
Q

Forward Bias

A

Junction voltage opposes the supply battery voltage
As supply voltage increases majority charge carriers are able to flow
When p type material is connected to the positive of the supply
Electrons at that side have less potential energy than under no bias
Lowers bands on p-type side
Conduction can take place

42
Q

Points about LED’s

A

Efficient light production as little heat produced
Low power devices - Work on small voltages
Protected by a resistor connected in series

43
Q

Monochromatic Light has

A

One energy, one frequency, one wavelength, one colou

44
Q

Why light produced is not completely monochromatic

A

Some electrons will fall from bands above the bottom of the conduction band to lower bands than the top of the valence band
These electrons undergo a greater energy transition
Resulting photon will be of greater frequency
Light produced nearer to blue end of spectrum

45
Q

Difference between circuit symbols of LED’s and Photodiodes

A

LED’s have arrows outwards - Light out

Photodiodes have arrows inwards - Light shining onto

46
Q

Voltage against light level graph (Solar Cell)

A

Output voltage quickly rises and remains constant
While voltage quickly reaches a maximum the same is not true of current delivered
When light level is increased the current delivered by the cell continues to rise

47
Q

Differences in design of LED’s and Photodiodes

A

P-type section at the top of the photodiode is much thinner
N-type covered with a material which transmits light
Both of these maximise light reaching the junction region

48
Q

Photovoltaic Mode

A

Photodiodes can be used to provide energy for solar powered equipment eg calculators
Photodiode is the power supply and so does not require a bias voltage
Amount of energy available depends upon area exposed to the light and on the intensity and frequency of the light source

49
Q

What is the overall charge on an unbiased piece of semi conductor material?

A

Neutral

50
Q

The number of valence shell electrons in a
N-type
Pure Semiconductor
P-Type

A

5 in n-type
4 in pure semiconductor
3 in p-type

51
Q

Bias conditions required for an LED to emit light

A

Forward Bias

52
Q

The farad is equivalent to the

A

Coulomb per volt

53
Q

Changing the resistance in a circuit with a capacitor

A

Has no effect on the maximum energy stored as C and V are still the same

54
Q

Connecting resistors to give max and min resistance

A

Max - Series

Min - Parallel

55
Q

Explain in terms of charge carriers how an LED emits light

A

Electrons in n-type material combine with holes in p-type material, they lose energy as they cross the junction. This energy is emitted as quanta of visible radiation.

56
Q

Capacitor Facts

A

Used to block DC signals
Can be used to store energy
Can store electric charge

Higher Physics (11 decks)

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