Flashcards
P2 Electricity
Cards in this deck (53)
- 1How do objects get electrostatically charged?When certain insulating materials are rubbed against each other they become electrically charged. Negatively charged electrons are rubbed off one material and onto the other.
- 2How do objects get a negative or positive charge?The material that gains electrons becomes negatively charged. The material that loses electrons is left with an equal positive charge.
- 3Rules for attraction and repulsion for electrostatic chargeWhen two electrically charged objects are brought together they exert a force on each other.
Two objects that carry the same type of charge repel. Two objects that carry different types of charge attract. - 4Materials that charge can flow throughConductors, metals
- 5What is electric current? How is it calculated?Electric current is a flow of electric charge. The size of the electric current is the rate of flow of electric charge. The size of the current is given by the equation:
I=Q/t - 6What is potential difference? How is it calculated?The potential difference (voltage) between two points in an electric circuit is the work done (energy transferred) per coulomb of charge that passes between the points:
V=W/Q - 7How are thermistors used in circuits?To detect temperature, eg digital thermometer, thermostat
- 8How are LDRs used in circuits?To detect light intensity, eg switching light on at night, light sensor on (phone) camera
- 9What is a current-voltage graph?Current–potential difference graphs are used to show how the current through a component varies with the potential difference across it.
- 10The current–potential difference graph for a resistor at constant temperature.
- 11How to measure the resistance of a componentThe resistance of a component can be found by measuring the current through, and potential difference across, the component.
- 12How are current and voltage linked for a resistor (at constant temperature)?The current through a resistor (at a constant temperature) is directly proportional to the potential difference across the resistor.
- 13Equation linking current, voltage and resistanceCalculate current, potential difference or resistance using the equation:
V=I×R - 14The effect of adding cells in series?The potential difference provided by cells connected in series is the sum of the potential difference of each cell (depending on the direction in which they are connected).
- 15Patterns for series circuits (Current, voltage, resistance)For components connected in series:
■ the total resistance is the sum of the resistance of each component
■ there is the same current through each component
■ the total potential difference of the supply is shared between the components. - 16Patterns for parallel circuits (Current, voltage)For components connected in parallel:
■ the potential difference across each component is the same
■ the total current through the whole circuit is the sum of the currents through the separate components. - 17Voltage-current graph for a filament bulb?
- 18How does resistance change for a filament bulb as the temperature of the filament increases?The resistance of a filament bulb increases as the temperature of the filament increases.
- 19Why does the resistance of a filament bulb increase as the temperature of the filament increases. (H)More atom (ion) movement in metals, so electrons collide more often, so lose more energy, so less current flow per volt.
- 20Voltage-current graph for a diode?
- 21Describe current flow in a diodeThe current through a diode flows in one direction only. The diode has a very high resistance in the reverse direction.
- 22How does an LED work?An LED emits light when a current flows through it in the forward direction.
- 23How does the resistance of an LDR vary?The resistance of a light-dependent resistor (LDR) decreases as light intensity increases.
- 24How does the resistance of a thermistor vary?The resistance of a thermistor decreases as the temperature increases.
- 25What is dc? What items supply it?Cells and batteries supply current that always passes in the same direction. This is called direct current (d.c.).
- 26What is ac?An alternating current (a.c.) is one that is constantly changing direction.
- 27Candidates should be able to compare and calculate potential differences of d.c. supplies and the peak potential differences of a.c. supplies from diagrams of oscilloscope traces.Well, can you?
- 28Higher Tier candidates should be able to determine the period and hence the frequency of a supply from diagrams of oscilloscope traces.Well, can you?
- 29Mains electricity voltage and frequency?Mains electricity is an a.c. supply. In the UK it has a frequency of 50 cycles per second (50 hertz) and is about 230 V.
- 30The structure of electrical cable.
- 31The structure and wiring of a three-pin plug.
- 32What is a fuse or circuit breaker for?If an electrical fault causes too great a current, the circuit is disconnected by a fuse or a circuit breaker in the live wire.
- 33How does a fuse work?When the current in a fuse wire exceeds the rating of the fuse it will melt, breaking the circuit.
- 34What is an RCCB?Candidates should realise that RCCBs operate by detecting a difference in the current between the live and neutral wires. Knowledge of how the devices do this is not required.
Candidates should be aware of the fact that this device operates much faster than a fuse. - 35What extra safety 'device' is used for metal-cased appliances?Appliances with metal cases are usually earthed.
- 36What appliances do not need an earth wire?Candidates should be aware that some appliances are double insulated, and therefore have no earth wire connection.
- 37Link between cable thickness and fuse value?Thicker wire can carry higher current safely, so will tend to be fitted with higher rating fuses
- 38What does a flow of charge do to a resistor?When an electrical charge flows through a resistor, the resistor gets hot.
- 39Link between power, energy and time?The rate at which energy is transferred by an appliance is called the power.
P=E/t - 40Link between power, voltage and current (equation)?Power, potential difference and current are related by the equation:
P=I×V - 41—Switch
- 42—Cell
- 43—Battery
- 44—Diode
- 45—Resistor
- 46—Variable resistor
- 47—LED
- 48—Lamp
- 49—Fuse
- 50—Voltmeter
- 51—Ammeter
- 52—Thermistor
- 53—LDR
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- Flashcards on P2 Electricity, created by dfreeman on 16/05/2014.
- Created by
- dfreeman · May 2014
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- Dec 19, 2016
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