Topic 2- Electricity Flashcards
What is electric current?
The flow of electrical charge
What can be said abut current at any point in a single closed loop?
It is the same al every point in the circuit
What 2 factors does current in a circuit depend on?
- Potential difference
2. Resistance
What is an ohmic conductor?
A conductor for which potential difference and current are directly proportional.
Resistance remains the same as current changes
Temperature must be constant
List 4 components for which resistance is not constant as current changes (non-ohmic conductor)
- Lamp
- Diode
- Thermistor
- Light dependent resistor
What happens to resistance of filament lamp as temp increases and why?
Resistance increases.
Ions in metal have more energy- vibrate more- more collisions with electrons as flow through metal- greater resistance to current flow
What is different about current flow through a diode?
Current only flows in one direction. This is because resistance is high in other direction and prevents current flow
What happens to resistance of thermistor as temperature increases?
Resistance decreases
Give 2 examples of when a thermistor may be used
- Thermostat to turn heater on below certain temperature
2. Freezer to turn cooler on when temperature becomes to high
What happens to the resistance of an LDR as light intensity increases?
Resistance increases
State a use of an LDR
Street lights- when light level becomes too low, light gains sufficient current to turn on
What are 2 ways for a component to be connected to a circuit?
In series and in parallel
How does PD vary when connected in series and in parallel?
Series; total PD shared between component
Parallel; PD across each component is the same
If 2 resistors are in parallel, what can be said about their combined total resistance?
Total resistance is less than the resistance of the smallest resistor
If 2 resistors are in series, what can be said about their combined total resistance?
Total resistance is equal to the sum of the individual resistances
Describe the current in a series circuit?
Same at every point as it only has on path to follow
Describe current in a parallel circuit
Current shared between different branches. Charge splits when it reaches a junction
How should you connect an ammeter in a circuit?
Connect in series with component they are messing current through
How should you connect a voltmeter in a circuit?
Connect in parallel to component they are measuring PD of
Why is it better to connect lamps in parallel?
If one lamp blows, the rest will remain unaffected and can still receive current (circuit still complete)
Is mains AC or DC?
Alternating current (AC)
Define alternating and direct current.
AC: current that continuously changes direction at a specific frequency
DC: one directional current flow
What is the frequency and voltage of the UK mains supply?
230V, 50Hz
What are the wires in the cables that connect electrical appliances to the mains?
- Earth wire
- Live wire
- Neutral wire
What is insulation colour used on earth wire?
Green and yellow stripes
What is the insulation colour used on the live wire?
Brown
What is the insulation colour used on the neutral wire?
Blue
When doesn’t the earth wire carry a current?
Under normal circumstances- doesn’t carry current
If fault occurs in appliance (casing becoming live) current will flow to ground
What potential is the neutral wire?
0V
What is PD between earth and live wires?
230 V
What is the purpose of the neutral wire?
Completes circuit by connecting it back to mains supply
For metal appliances, where is the earth metal connected to?
Metal casing of appliance
If live wire becomes lose and touches casing, current will flow through to prevent electrocution
What factors does the amount of energy transferred by an appliance depend on?
- How long appliance is being used for
2. Power of the appliance
Describe energy transfers in a battery powered torch?
Battery converts Chemical energy converted into electrical energy
Bulb converts electrical energy into light (and heat- watse)
What 3 things determine power of a circuit device?
- PD across circuit
- Current through circuit
- Amount of energy transferred in a given time
What is purpose of the national grid?
Link power statins to consumers so they have an electricity source
What are the function of step up transformers?
Increase PD from power station to transmission cables
What is the function of step down transformers?
Decrease PD from transmission cables to domestic buildings
Why is PD raised?
High PD= low current
Lower the current, less energy is wasted as heat, so more efficient
Why does PD then need to be decreased?
Safer- reduces risk of electrocution- appliances only designed for 230 V
