Electricity Flashcards
How do you draw fuses, diodes, variable resistors, thermistors, LEDs and LDRs.
Practice sketching and check.
RP3. Use circuit diagrams to set up and check appropriate circuits to investigate the factors affecting the resistance of electrical circuits. This should include:
the length of a wire at constant temperature.
- Set up battery, ammeter and wire in series and a voltmeter in parallel.
- Attach two crocodile clips at 0cm and 10cm down the wire.
- Record current and potential difference, increasing the gap between the crocodile clips by 10 cm up to 1 metre.
- Use the equation R = V/I to find the resistances of the wire.
- Plot a graph of resistance against length for the resistance wire. The relationship should be directly proportional.
Systematic errors: voltmeter and ammeter zero errors.
Random errors: the voltmeter reading fluctuated, incorrectly measured length of wire.
Hazards: Heating of the resistance wire + high current.
Risks: Skin burns + heating and melting of wire.
Precautions: Don’t touch the wire while the circuit is on, allow the wire time to cool + use low currents.
RP3. Use circuit diagrams to set up and check appropriate circuits to investigate the factors affecting the resistance of electrical circuits. This should include:
combinations of resistors in series and parallel.
- Set up two equal resistors, battery and ammeter in series with a voltmeter in parallel across both resistors. Set the voltage to 6V.
- Measure current and voltage, calculate total resistance.
- Repeat with three equal resistors in series. Resistance will increase because there is only one path for current to follow, and it will experience more resistance. Current is consistent through components, voltage is shared across both components. Resistance is the sum of the individual resistances.
- Repeat but with two equal resistors in parallel.
- Repeat with three resistors in parallel, this value will be less than the resistance of the previous parallel circuit because there will be more paths for the current to follow. Current is split between components, voltage supplied is equal to all components. Resistance is less than the resistance of the smaller resistor.
Systematic error: zero error
Random error: misreads, fluctuating values
Hazards: Hot wires
Risks: Minor burns
Precautions: Set up circuit before closing switch
Why does resistance change in non ohmic conductors.
As current increases the ions in the metal vibrate more vigorously and gain kinetic energy, therefore gaining temperature. The metal ions and electrons bump into each other more, which increases resistance.
Give examples of non-ohmic conductors, and why they are useful.
Lamps and diodes. Thermistors can be used as thermostats as their resistance decreases as temperature increases. LDRs can be used to switch on lights as their resistance decreases, current increases and potential difference decreases as light intensity increases.
RP4. Use circuit diagrams to construct appropriate circuits to investigate the I–V characteristics of a variety of circuit elements, including a filament lamp, a resistor and a diode at constant temperature.
- Set up a circuit so that there is a battery, ammeter, variable resistor and resistor in series with a voltmeter in parallel across the resistor. Set the variable resistor so that ammeter and voltmeter readings are 0.
- Adjust the variable resistor and take 5 readings then swap the battery terminals, set the variable resistor so that the readings are 0, then take a further 5 readings of negative numbers.
- Repeat with a bulb instead of a resistor.
- Plot graphs of current against pd. The fixed resistor will have a directly proportional relationship, and therefore it is ohmic. The bulb will plot a non-directly-proportional curve as it is a non-ohmic component.
- Set up the same circuit but with an additonal protective resistor between 100 and 500 ohms.
- Repeat above step 2.
- Plot a graph for the diode. Current only flows in one direction, in the other direction when voltage is trying to push the current the wrong way the diode’s resistance will be very high so no current can flow. When in the right direction, the diode’s resistance drops quickly from very high to very low and current flows. At a certain point the diode will burn out and current will return to 0.
Systematic error: zero error
Random error: measurements, fluctuations
Hazards: heated wire.
Risks: skin burns.
Precautions: don’t touch the resistance wire while the circuit is on and allow it to cool.
Equivalent resistance concept just means…
The total resistance of resistors.
Explain the design and use of dc series circuits for measurement and testing purposes.
Analyse component behaviour, verify circuit properties, and diagnose circuit issues.
What are the three properties of UK mains electricity and why?
50Hz, ac for efficiency and 230V as it is safe but substantial.
In a three-core cable, what are the wires, their functions, colours, voltage and why.
The earth green and yellow wire provides an alternate pathway to the earth for the current in case there is a fault. (0V)
The live wire is brown. (230V)
The neutral wire is blue. (0V approx)
Explain how the transfer of electrons between objects can explain the phenomena of static electricity with an example.
An insulator like hair rubs against a balloon, and becomes charged. The hairs repel each other as they are all positively or negatively charged.
Why does sparking occur, include fields?
If a charged object with a large surplus of electrons has a strong enough electric field, electrons will jump from it (charge is forced) to a neutral object across an insulator, there is a potential difference between the charged object and the neutral object. The charge earths.
Draw an electric field pattern for an isolated charged sphere.
Sketch and check.
