Topic P2 - Electricity Flashcards
Current definition
Flow of electrical charge
What is current measured in?
Ampere, A
Potential difference definition
Driving force that pushed charge round
What is potential difference measured in?
Volt, V
Resistance definition
Anything that slows down charge flow
What is resistance measured in?
Ohm, Ω
Current through a component depends on two factors:
1)
The component’s resistance
- The greater the resistance, the smaller the current.
2)
The potential difference across the component.
- The greater the potential difference, the larger the current (for a fixed resistance).
Size of current = rate of…
Size of current = rate of flow of charge
Charge flow formula
Q = It
Q - charge flow (C)
I - current (A)
t - time (s)
What is charge flow measured in?
Coulombs, C
Potential difference equation
V = IR
V - Potential Difference (V)
I - Current (A)
R - Resistance (Ω)
For circuit symbols look at page 83.
For circuit symbols look at page 83.
What are the 3 different I-V characteristics?
1) Ohmic conductors at constant temperature
2) Filament Lamp
3) Diode
I-V ohmic conductor at constant temperature graph characteristics
Current is directly proportional to potential difference so resistance doesn’t change.
Current is directly proportional to potential difference…
…so resistance doesn’t change
Is an ohmic conductor I-V graph liner or non-linear?
Linear
What are 4 examples of components with changing resistances when the current through them varies?
1) Filament Lamp
2) Diode
3) LDR
4) Thermistor
I-V, filament lamp graph characteristics
Current increase so temperature of filament increases so resistance increases.
I-V, diode graph characteristics.
High resistance in one direction so current only flows in the other direction.
Are filament lamps and diode graphs linear or non-linear.
Non-linear
An LDR resistance depends on?
Light intensity
An LDR has lower resistance in?
Brighter light
LDRs are used in?
Automatic night lights
A thermistors resistance depends on?
Temperature
A thermistors has lower resistance in?
Hotter temperatures
Thermistors are used in?
Thermostats
What are the 2 types of electricity supply?
1) Alternating current
2) Direct Current
Alternating current (ac) definition
Current that constantly changes direction and is produced by an alternating voltage. Used in mains supply.
Direct Current (dc) definition
Current that always flows in the same direction and is produced by a direct voltage. Supplied by batteries.
When charge flows, work is done and so…
When charge flows, work is done and so energy is transferred
How is energy transferred from a plug socket to a kettle?
Energy is transferred electrically, to thermal energy store of the heating element inside the kettle.
How is energy transferred from a battery to a fan?
Energy is transferred electrically, the the kinetic energy store of the fan’s motor.
Energy transfer formulas
E = QV
E = Pt
E - energy transferred ( J ) Q - charge flow (C) V - Potential Difference (V) P - power (W) t - time (s)
Amount of energy an appliance transfers depends on:
- appliance’s power
- how long appliance is on for
Power definition
Energy transferred per second
Power rating definition
Maximum safe power an appliance can operate at.
Power formulas
P = VI
P = I²R
P - power (W)
V - potential difference (V)
I - current (A)
R - resistance (Ω)
National grid definition
A system of cable and transformers that connect power stations to consumers
What does a step-up transformer do?
Increases potential difference
What does a step-down transformer do?
Decreases potential difference
How can electrical power be transferred efficiently?
High potential difference and a low current.
What would happen if electrical power was transferred at a high current?
Wires would heat up and transfer a lot of energy to the thermal energy stores of the surroundings.
Density formula
p = m/v
p - density (kg/m³)
m - mass (kg)
v - volume (m³)
What is density’s unit?
kg/m³
What can increased internal energy of a system do?
1) Increase temperature
2) Change in state
The higher the temperature of a gas, the higher the average energy…
In the kinetic energy stores of the gas particles
Gas pressure is caused by…
Gas particles colliding with a surface and exerting a net force on it.
If a gas at a constant volume has a temperature increase what will happen?
Gas particles get faster and collide with the container more often, leading to a pressure increase
