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AS Physics > G482 - Electricity > Flashcards

G482 - Electricity Flashcards

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0
Q

Charge

Definition

A

An inherent property of some particles leading to forces of attraction and repulsion
Measured in coulombs

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1
Q

Electric Current

Definition

A

A flow of charge
A vector quantity
Measured in Amperes, A

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2
Q

Charge

Formula

A

Charge (coulombs) = Current (A) x Time (s)

Q = It

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3
Q

Coulomb

Definition

A

A unit of electrical charge

One coulomb of charge is carried by one amp of current in one second

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4
Q

Ammeter

A

Used to measure electric current
Connected in series
Must have negligible resist have so that they don’t reduce the current reading

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5
Q

Charge Carriers

In Metals

A

Electrons

Electric current in a metal is the flow of electrons

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6
Q

Charge Carriers

In Electrolytes

A

Ions

Electric current in electrolytes is the flow of ions

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7
Q

Electrolyte

Definition

A

A fluid that contains ions that are free to move and therefore conduct electricity

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8
Q

Conventional Current

Definition

A

Current flow is taken to be the direction of flow from positive to negative

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9
Q

Electron Flow

Definition

A

The actual movement of electrons in a metal and the direction of current flow, from negative from positive

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10
Q

Elementary Charge

Definition

A

The charge on one electron

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11
Q

Elementary Charge

Value

A

1.6 x 10^-19

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12
Q

Amp

Definition

A

Unit of electric current

One amp of current means one coulomb of charge passes a point per second

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13
Q

Kirchoff’s First Law

A

Conservation of charge

The sum of the currents flowing into a point in a circuit is equal to the sum of the currents leaving that point

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14
Q

Drift Velocity

Definition

A

The average velocity of an electron as it travel through a wire due to potential difference

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15
Q

Drift Velocity

Formula

A

v = I / Ane

v = drift velocity (m/s)
I = current (A)
A = cross sectional area of wire (m²)
n = number density
e = elementary charge
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16
Q

Number Density

Conductor

A

Huge number of free conduction electrons

Large number density

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17
Q

Number Density

Insulators

A

An effective insulator has very few conduction electrons

Number density close to zero

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18
Q

Number Density

Semiconductors

A

Intermediate properties

Intermediate number density

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19
Q

Potential Difference

Definition

A

The electrical energy transferred per unit charge when electrical energy is converted into some other form of energy
Work done moving charges around the circuit, energy used within the circuit

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20
Q

Electromotive Force

Definition

A

The electrical energy transferred per unit charge when one form of energy is converted into electrical energy
Energy supplied to the circuit

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21
Q

Energy

Formula

A

Energy (J) = P.D. (V) x Charge (coulombs)

W = VQ

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22
Q

Volt

Definition

A

Unit of potential difference

One volt means one joule of energy transferred per coulomb of charge

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23
Q

Voltmeter

A

Measures potential difference
Connected in parallel across a component to measure the potential difference across it
Must have a high resistance so that current flows through the circuit rather than the voltmeter

24
Q

Resistance

Definition

A

A property of a component that regulates the electric current through it
Measured in ohms, Ω

25
Q

Resistance

Formula

A

Resistance (Ω) = Voltage (V) / Current (I)

R = V / I

26
Q

Ohm’s Law

A

For some metallic conductors maintained at a constant temperature and with all other conditions constant, the potential difference divided by the current is a constant
Materials that obey Ohm’s Law are called ohmic conductors

27
Q

Benefits of LEDs

A 
Switch in instantly
Very robust
Very versatile
Operate on low p.d.s
Have a long working life
28
Q

Ohm

Definition

A

Unit of resistance

One ohm means one volt per amp

29
Q

Resistivity

Definition

A

A property of a material that regulates the flow of current rather than a property of a component

30
Q

Resistivity

Formula

A

ρ = RA / l

ρ = resistivity (Ωm)
R = resistance (Ω)
A = cross sectional area (m²)
l = length of wire (m)
31
Q

Resistivity

Metals and Temperature

A

Increasing the temperature gives the atoms in the metal more kinetic energy
This causes the atoms to vibrate and move around making it more difficult for charge carrying electrons to move past them
The resistance has increased and therefore so has the resistivity as ρ = RA / l
The heat energy allows electrons to move within the conduction band but the gap between the valence band and the conduction band is too big for more electrons to pass from the valence band to the conduction band with this energy

32
Q

Resistivity

Semi Conductors and Temperature

A

Increasing temperature increases the number of charge carriers as the heat energy allows electrons to move from the valence band across a gap to the conduction band, in semiconductors this gap is very small
There are more charge carriers available so resistance decreases as temperature increase

33
Q

Resistivity

Negative Temperature Coefficient Thermistors (NTC)

A

NTCs are semiconductors
This means that as temperature increase their resistance decreases
This is what allows them to act as temperature sensors

34
Q

Superconductivity

A

A superconductors resistance will suddenly drop to 0 at its critical temperature
This temperature is very low

35
Q

Power

Definition

A

The rate of doing work or the rate of energy transfer
A scalar quantity
Measured in watts, W

36
Q

Power

Formulae

A

P = VI = I²R = V² / R

P = power (W)
V = voltage (V)
I = current (A)
R = resistance (Ω)
37
Q

Watt

Definition

A

Unit of power

One watt means that one joule of energy is transferred per second

38
Q

Work Done

Definition

A

The energy converted from one form to another
Or the product of a force and the distance moved in the direction of the force
A scalar quantity
Measured in Joules, J

39
Q

Work Done or Energy

Formula

A

W = Pt = IVt

W = work done or energy (J)
P = power (W)
t = time (s)
I = current (A)
V = voltage (V)
40
Q

Joule

Definition

A

Unit of energy

One joule is the energy transferred or work done by one watt in one second

41
Q

Fuses

Purpose

A

Prevent overloading

42
Q

Fuses

How they work

A

Consist of a copper wire in a ceramic casing
If a certain current passes through the wire it is so thin that it would melt, breaking the circuit
Different fuses melt at different currents
A fuse should be rated above the maximum current drawn from a device calculated using its power rating and the voltage through it, P=IV

43
Q

Fuses

Most Common in Household Appliances

A

3A and 13A fuses

44
Q

Kilowatt Hour

Definition

A

A unit of energy used by electricity companies as they deal in such large amounts
One kWh means 1000W used for 3600 seconds which is equivalent to 3600000 joules

45
Q

Mains Voltage

Value

A

230V

46
Q

Series Circuit

Definition

A

Components are connected end to end therefore only providing one oath for current to flow along

47
Q

Parallel Circuit

A

Components are connected in two or more branches therefore providing multiple paths for current

48
Q

Kirchoff’s Second Law

A

Conservation of energy
In any closed loop circuit the sum of the e.m.f.s (energy supplied to the circuit) is equal to the sum of the p.d.s (energy used in the circuit)

49
Q

Internal Resistance

Definition

A

All sources of e.m.f have a small internal resistance, r, as they are made from materials with electrical resistance

50
Q

Terminal P.D.

Definition

A

The e.m.f. of a cell of battery when it is not supplying a circuit

51
Q

Lost Volts

Definition

A

Some energy is lost as heat in the battery, it behaves as if it has internal resistance

52
Q

EMF

Formula

A

E = V + Ir = I (R + r)

E = e.m.f (V)
V = voltage (V)
I = current (A)
R = resistance in the circuit (Ω)
r = internal resistance (Ω)
53
Q

Potential Divider

Definition

A

A type of circuit containing two components designed to divide up the p.d. in proportion to the resistances of the components

54
Q

Potential Divider V1

Formula

A

V1 = (R1 / (R1+R2)) x Vin

V1 = voltage across R1 (V)
R1 = resistance of first resistor (Ω)
R2 = resistance of second resistor (Ω)
Vin = input voltage (V)
55
Q

Potential Divider V2

Formula

A

V2 = (R2 / (R1+R2)) x Vin

V2 = voltage across R2 (V)
R1 = resistance of first resistor (Ω)
R2 = resistance of second resistor (Ω)
Vin = input voltage (V)
56
Q

Light Dependent Resistor (LDR)

Light and Resistance

A

When the light level falls the resistance of the LDR increases
When the light level increases the resistance of the LDR decreases

57
Q

Advantages of Data Loggers

A

Can take lots of readings in a short space of time
Removes human error
Can simultaneously record readings e.g. voltage and current
Can take readings at precise intervals
Can display data as a graph on a computer

AS Physics (4 decks)

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