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Higher Physics > Electricity > Flashcards

Electricity Flashcards

(56 cards)

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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

Study These Flashcards
A

Flashing indicators

24
Q

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

Study These Flashcards
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
Metals are
Good conductors | Highest occupied band is not completely full - Conduction Band
26
In an insulator
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
In a semiconductor
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
An increase in temp in a semi conductor
Increases the conductivity of the semi conductor
29
An electron is a (Pn junctions)
Negative charged carrier
30
A hole is a
Positive charged carrier | A position where an electron is missing
31
n-type semiconductor
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
p-type semi-conductor
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
All n-type and p-type conductors are
Electrically neutral
34
Hole movement really is
The movement of electrons filling holes and leaving new ones in the atom they came from
35
Doping has the effect of
Lowering the resistance of the semiconductor
36
Depletion Layer
The area surrounding the p-n junction of a diode Electrons have combined with holes No excess charges
37
As bias voltage is increased
Current through the diode will also increase Current IS NOT directly proportional to the voltage Diodes referred to as 'non-ohmic' conductors
38
When supply voltage is greater than depletion layer voltage - Forward Bias only
Free electrons in n-type conduction band can be pushed across the depletion layer Up into conduction band of p-type semi-conductor
39
Leakage current
The tiny amount of current in a reverse-biased diode
40
Reverse Bias
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
Forward Bias
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
Points about LED's
Efficient light production as little heat produced Low power devices - Work on small voltages Protected by a resistor connected in series
43
Monochromatic Light has
One energy, one frequency, one wavelength, one colou
44
Why light produced is not completely monochromatic
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
Difference between circuit symbols of LED's and Photodiodes
LED's have arrows outwards - Light out | Photodiodes have arrows inwards - Light shining onto
46
Voltage against light level graph (Solar Cell)
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
Differences in design of LED's and Photodiodes
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
Photovoltaic Mode
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
What is the overall charge on an unbiased piece of semi conductor material?
Neutral
50
The number of valence shell electrons in a N-type Pure Semiconductor P-Type
5 in n-type 4 in pure semiconductor 3 in p-type
51
Bias conditions required for an LED to emit light
Forward Bias
52
The farad is equivalent to the
Coulomb per volt
53
Changing the resistance in a circuit with a capacitor
Has no effect on the maximum energy stored as C and V are still the same
54
Connecting resistors to give max and min resistance
Max - Series | Min - Parallel
55
Explain in terms of charge carriers how an LED emits light
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
Capacitor Facts
Used to block DC signals Can be used to store energy Can store electric charge

Higher Physics (11 decks)

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