P2: Electricity Flashcards
Describe how you could investigate how the pd through a filament lamp affects its current.
- Attach in series a variable resistor, ammeter, and bulb, and a voltmeter in parallel with the bulb.
- Take current readings with the ammeter as you alter the pd across the bulb (measured with the voltmeter) using the variable resistor.
- Turn the circuit off between readings to stop the wire heating up.
- Plot the pd (independent variable) against the current (dependent variable) on a graph.
- Control variables: component under investigation, type of wire, cell/battery and other components.
Draw a circuit diagram with a cell, bulb, ammeter and a voltmeter
The voltmeter always goes on a seperate loop (branch) to the bulb. The ammeter is in the same loop
What is the green + yellow wire?
Earth
What happens if you touch the live wire?
- A large pd is produced across your body
- A current flows through you
- Causes an injuring/lethal electric shock
What is the purpose of the live wire?
Provides the alternating potential difference flowing to the fuse.
What is charge flow?
The total charge which has passed through a circuit in a given time.
What is current?
Rate of flow of charge.
What is the blue wire?
Neutral
What is direct current (d.c.)?
- Current flows in one direction around the circuit, due to a direct pd.
- Supplied by cells and batteries.
What colour is the earth wire?
Green + yellow
Give three uses of LDRs.
- Automatic night lights
- Outdoor lighting
- Burglar detectors.
What is the unit for charge flow?
Coulombs (C)
Describe how you would investigate how wire length affects resistance.
- Connect an ammeter in series with a test wire, using crocodile clips to attach the wire to the test wire. Connect a voltmeter in parallel to the test wire.
- Place the 0cm mark on a metre ruler level with one clip, and attach the other clip a set distance away, recording the length of the wire between the clips.
- Record the current through the wire (ammeter) and pd across it (voltmeter).
- Open the switch and move the 2nd clip further down the metre ruler, again measuring the length between clips. Repeat step 3 with several different wire lengths.
- Turn off the circuit between readings to stop the wire heating.
- Use R = V/I to calculate the resistance for each length of wire, then plot the wire length against resistance. The graph should show a directly proportional relationship.
What equation links voltage, current and resistance?
V = IR
Describe how the graph for an ohmic conductor would look. What would this show?
It would be a straight line which passes through the origin ([0,0]).
This shows that, at a constant temperature, the current flowing through an ohmic conductor is directly proportional to the pd across it.
What is the frequency of UK mains electricity?
50Hz.
As temperature increases, the resistance of thermistors __ - and vice versa.
As temperature increases, the resistance of thermistors decreases - and vice versa.
What is potential difference?
Energy transferred per unit charge.
What are ohmic conductors?
Components which follow Ohm’s law (V=IR). This includes wires and resistors. Their resistance is constant and doesn’t vary with current.
Draw the circuit symbol for a fuse
Draw the circuit diagram for an ammeter
Why do we need step-down transformers?
Electricity has to be reduced to mains pd (230V) to be safe and usable.
Draw the electric field around a negative charge
Draw a cell symbol
What is power and its unit and symbol?
Rate of energy transfer to charges. Unit = watts (W); symbol = P.
Draw the circuit symbol for a diode
Draw the IV graph for a diode
What happens at step-down transformers?
Pd lowered, current increased.
What equation links energy, voltage and charge flow?
Energy = charge x potential difference
What happens at step-up transformers?
Pd increased, current lowered.
Draw the IV graph for a filament lamp
What is the brown wire?
Live
What is the purpose of the earth wire?
Protects the circuit and stops the appliance casing from becoming live. Only carries current if there is a fault.
Draw the circuit symbol for a light emitting diode (LED)
Draw the circuit symbol for a thermistor
UK mains supply is at __V to -__V.
- 230
- -230
What is the unit for resistance?
The ohm (Ω).
Draw the circuit symbol for resistor
Draw the circuit symbol for a battery
Draw the circuit symbol for a light dependent resistor (LDR)
What is alternating current (a.c.)?
- Current alternates direction.
- Caused by a pd where the positive and negative ends alternate.
What colour is the neutral wire?
Blue
The length of a wire is directly proportional to its what?
Resistance.
UK mains electricity is an __ supply.
A.c.
Draw the circuit symbol for a lamp (bulb)
What colour is the live wire?
Brown
What equation links current, time and charge flow?
charge = current x time
What is the purpose of the neutral wire?
Completes the circuit; carries current away.
What is resistance? What causes it?
Something that opposes flow of charge, transferring energy away as heat.
Caused by electrons colliding with each other and the wire.
What is the national grid?
A system of cables and transformers, transferring electrical power from stations to consumers.
Draw the circuit symbol for a voltmeter
