Physics Unit 5: Electricity
- Created by: NiamhM1801
- Created on: 18-02-17 10:46
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- Electricity
- Potential Difference
- Measured in volts, V
- One volt is one joule per coulomb
- Using a voltmeter
- Should always be placed in parallel with the component it is measuring
- Defined as "the work done per unit charge"
- V = W/Q (Potential difference (V) = Work Done (J) / Charge (Q)
- Measured in volts, V
- Resistance
- A measure of how difficult it is to get current to flow through a component
- Measured in ohms, ?
- R = V/I (Resistance (?) = Potential Difference (V) / Current (I)
- Potential Difference
- Measured in volts, V
- One volt is one joule per coulomb
- Using a voltmeter
- Should always be placed in parallel with the component it is measuring
- Defined as "the work done per unit charge"
- V = W/Q (Potential difference (V) = Work Done (J) / Charge (Q)
- Measured in volts, V
- Current
- Measured in amps, A
- One amp is one coulomb per second
- Using an ammeter
- Should always be placed in series with the component it is measuring
- Defined as the "rate of flow of charge"
- I = Q/t (Current (A) = Charge (Q) / time (s))
- The unit of charge is called a Coulomb
- One coulomb is defined as "the amount of charge that passes in one second if the current is 1 amp"
- One amp is one coulomb per second
- The unit of charge is called a Coulomb
- Measured in amps, A
- Potential Difference
- Ammeters and voltmeters are treated as ideal - they have zero and infinite resistance respectively
- Affected by
- Resistivity
- ? = RA/L (resistivity (ohm-meters) = Resistance (ohms) x cross sectional area (metres squared) / length (m)
- Temperature
- Length of wire
- Cross-sectional area of wire
- Resistivity
- Current
- Measured in amps, A
- Using an ammeter
- Should always be placed in series with the component it is measuring
- Using an ammeter
- Defined as the "rate of flow of charge"
- I = Q/t (Current (A) = Charge (Q) / time (s))
- The unit of charge is called a Coulomb
- One coulomb is defined as "the amount of charge that passes in one second if the current is 1 amp"
- The unit of charge is called a Coulomb
- Measured in amps, A
- I-V Characteristics
- Ohmic Conductors
- Graph is linear - direct proportionality
- On an I/V graph, a steep gradient means low resistance
- On a V/I graph, a steep gradient means high resistance
- Obey Ohm's Law
- States that, provided physical conditions such as temperature remain constant, the current is directly proportional to the potential difference
- Graph is linear - direct proportionality
- Filament Lamps
- Do not obey Ohm's Law
- Graph isn't linear - begins to curve
- I/V graph starts steep but gets shallower
- V/I graph starts shallow but gets steeper
- Because the temperature increases
- Increase in temperature causes an increase in resistance
- R = V/I
- V/I graph starts shallow but gets steeper
- R = V/I
- Increase in temperature causes an increase in resistance
- Graph isn't linear - begins to curve
- Graph isn't linear - begins to curve
- I/V graph starts steep but gets shallower
- Because the temperature increases
- Increase in temperature causes an increase in resistance
- R = V/I
- R = V/I
- Increase in temperature causes an increase in resistance
- Do not obey Ohm's Law
- Semi-conductors
- Diodes
- Do not obey Ohm's Law
- Only allow current to flow in one direction (forward bias)
- Resistance is very high in the reverse direction (reverse bias)
- So very little current can get through
- Have a threshold potential difference of about 0.6V in the positive direction
- Must be met before it will conduct
- Thermistors
- NTC (Negative Temperature Coefficient) thermistors react to temperature
- Increasing the temperature lowers the resistance
- NTC (Negative Temperature Coefficient) thermistors react to temperature
- Are much worse conductors of electricity than metals
- Because they have far fewer charge carriers available
- More charge carriers can be released using energy
- Because they have far fewer charge carriers available
- Very good sensors for detecting environmental change
- Diodes
- Ohmic Conductors
- Resistivity
- ? = RA/L (resistivity (ohm-meters) = Resistance (ohms) x cross sectional area (metres squared) / length (m)
- Power
- Defined as "the rate of energy transfer"
- Measured in Watts, W
- 1 Watt = 1 joule per second
- P = IV
- P = I^2R
- P = V^2/R
- P = I^2R
- Circuit Rules
- Resistance
- In series
- Adds up
- In parallel
- 1/RT = 1/R1 +1/R2...
- In series
- Potential Difference
- In series
- Adds up to match the p.d. of the cell
- In parallel
- Is the same everywhere
- In series
- Current
- In series
- Is the same everywhere
- In parallel
- Adds up to the total current
- In series
- Resistance
- Potential Difference
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