885999
| Question | Answer |
| How 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. |
| How 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. |
| Rules for attraction and repulsion for electrostatic charge | When 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. |
| Materials that charge can flow through | Conductors, metals |
| What 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 |
| What 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 |
| How are thermistors used in circuits? | To detect temperature, eg digital thermometer, thermostat |
| How are LDRs used in circuits? | To detect light intensity, eg switching light on at night, light sensor on (phone) camera |
| What 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. |
| The current–potential difference graph for a resistor at constant temperature. |
Image:
aqaaddsci_02.gif (image/gif)
|
| How to measure the resistance of a component | The resistance of a component can be found by measuring the current through, and potential difference across, the component. |
| How 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. |
| Equation linking current, voltage and resistance | Calculate current, potential difference or resistance using the equation: V=I×R |
| The 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). |
| Patterns 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. |
| Patterns 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. |
| Voltage-current graph for a filament bulb? | |
| How 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. |
| Why 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. |
| Voltage-current graph for a diode? | |
| Describe current flow in a diode | The current through a diode flows in one direction only. The diode has a very high resistance in the reverse direction. |
| How does an LED work? | An LED emits light when a current flows through it in the forward direction. |
| How does the resistance of an LDR vary? | The resistance of a light-dependent resistor (LDR) decreases as light intensity increases. |
| How does the resistance of a thermistor vary? | The resistance of a thermistor decreases as the temperature increases. |
| What 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.). |
| What is ac? | An alternating current (a.c.) is one that is constantly changing direction. |
| Candidates 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? |
| Higher Tier candidates should be able to determine the period and hence the frequency of a supply from diagrams of oscilloscope traces. | Well, can you? |
| Mains 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. |
| The structure of electrical cable. | |
| The structure and wiring of a three-pin plug. | |
| What 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. |
| How does a fuse work? | When the current in a fuse wire exceeds the rating of the fuse it will melt, breaking the circuit. |
| What 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. |
| What extra safety 'device' is used for metal-cased appliances? | Appliances with metal cases are usually earthed. |
| What appliances do not need an earth wire? | Candidates should be aware that some appliances are double insulated, and therefore have no earth wire connection. |
| Link between cable thickness and fuse value? | Thicker wire can carry higher current safely, so will tend to be fitted with higher rating fuses |
| What does a flow of charge do to a resistor? | When an electrical charge flows through a resistor, the resistor gets hot. |
| Link between power, energy and time? | The rate at which energy is transferred by an appliance is called the power. P=E/t |
| Link between power, voltage and current (equation)? | Power, potential difference and current are related by the equation: P=I×V |
|
Image:
switch.GIF (image/GIF)
|
Switch |
|
Image:
battery_cell.GIF (image/GIF)
|
Cell |
|
Image:
battery.GIF (image/GIF)
|
Battery |
|
Image:
diode.GIF (image/GIF)
|
Diode |
|
Image:
resistor_II.GIF (image/GIF)
|
Resistor |
| Variable resistor | |
|
Image:
led.GIF (image/GIF)
|
LED |
|
Image:
lamp.GIF (image/GIF)
|
Lamp |
|
Image:
fuse.GIF (image/GIF)
|
Fuse |
|
Image:
voltmeter.GIF (image/GIF)
|
Voltmeter |
|
Image:
ammeter.GIF (image/GIF)
|
Ammeter |
|
Image:
thermistor.gif (image/gif)
|
Thermistor |
| LDR |
Want to create your own Flashcards for free with GoConqr? Learn more.