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85 Cards in this Set
- Front
- Back
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What is static electricity? |
Static electricity is the build up of charges which are not free to move. This causes them to build up in one place where they stay until they are discharged (usually with a spark or a shock). |
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What is a build-up of static caused by? |
Friction. |
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What happens when certain insulating materials are rubbed together? |
Negatively charged electrons will be scraped off one object and transferred to the other. This leaves a positive static charge on one and a negative static charge on the other. |
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What will electrically charged objects do? |
Attract small objects placed near them. |
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True or false: |
True. Protons are fixed; +ve and -ve charges are only ever produced by the movement of electrons. |
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What is a positive static charge always caused by? |
The electrons moving away elsewhere. When a material loses electrons, there are more protons than electrons, which means that the overall charge of the material is positive. |
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Which type of material does electricity move easily through? Give an example. |
Conductors. Metals - like copper. |
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Which type of material does electricity NOT move easily through? Give an example. |
Insulators. Plastic is an example of an insulator. |
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What is current? |
The flow of electric charge round the circuit. |
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When will current flow? |
When there is a potential difference across that component. |
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What is the unit of measurement for current? |
Ampères/amps (A) |
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What is potential difference? |
The driving force that pushes current around the circuit. |
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When two insulators are rubbed together, which material will become negatively charged? Which material will become positively charged? |
The material that gains electrons will become negatively charged. The material that loses electrons will become positively charged. |
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When two electrically charged objects are brought together, what happens? |
They exert a force on each other. If their charges are opposite, they attract. If their charges are the same, they repel. |
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What is the size of current? |
The rate of flow of charge around a circuit. |
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What's the formula for size of current? |
Q --- = I t Charge in coulombs ------------------------------ = current time (s) |
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What is potential difference also known as? |
Voltage. |
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What is the potential difference between two points in an electric circuit? |
The work done (energy transferred) per coulomb of charge that passes between the points. |
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What is charge measured in? |
Coulombs (C) |
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Complete this sentence: More charge passes around the circuit when... |
...a bigger current flows. |
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What's the formula that relates potential difference, work done and charge? |
P.D. = Work done ---------------- Charge |
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What component in a circuit does this symbol represent? |
An open switch. |
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What component in a circuit does this symbol represent? |
A closed switch. |
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What component in a circuit does this symbol represent? |
A cell. |
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What component in a circuit does this symbol represent? |
A battery (of cells). |
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What component in a circuit does this symbol represent? |
A diode. |
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What component in a circuit does this symbol represent? |
A resistor. |
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What component in a circuit does this symbol represent? |
A variable resistor. |
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What component in a circuit does this symbol represent? |
An LED. |
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What component in a circuit does this symbol represent? |
A filament lamp. |
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What component in a circuit does this symbol represent? |
A fuse. |
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What component in a circuit does this symbol represent? |
A voltmeter. |
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What component in a circuit does this symbol represent? |
An ammeter. |
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What component in a circuit does this symbol represent? |
A thermistor. |
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What component in a circuit does this symbol represent? |
An LDR. |
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Why would you create a test circuit? |
So that you could find out the resistance of a component. |
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How do you measure the resistance of a component in a circuit? |
By measuring the current through and the potential difference across the component. |
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What is a V-I graph? |
Potential difference-current graph. |
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What do V-I graphs show? |
How current varies as you change the potential difference. |
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What does this graph show? Why do the lines have different gradients? |
The current through a resistor (at constant temperature) is directly proportional to voltage/potential difference. Different resistors have different resistances, which explains the different gradients. |
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What does this graph show? |
As the temperature of a filament lamp increases, the resistance increases. |
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What does this graph show? |
Current will only flow through a diode in one direction. The diode has high resistance in the direction that current DOES flow. |
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When the temperature of a component increases, what happens to the resistance? |
The resistance increases. |
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Why does increasing the temperature cause resistance to increase? |
The heat energy causes the ions in the conductor to vibrate more. This makes it more difficult for electrons to flow, meaning that charge can't flow as easily - this leads to resistance in the component increasing. |
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Why does the graph for the filament lamp level off at high currents? |
There is a limit to the amount of current that can flow through a component. More current means an increase in temperature, which means an increase in resistance, which means the current decreases again. |
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Why does the temperature of a component increase when an electrical charge flows through? |
Some of the electrical energy is transferred to heat energy. |
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What is the formula that relates potential difference, current and resistance? |
Potential difference = current x resistance |
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If a V-I graph has a straight line, what does this mean? |
The component is known as an 'ohmic conductor'. This means that the resistance of the component is steady and equal to the inverse of the gradient of the line. |
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In a V-I graph of an ohmic conductor, what does the gradient indicate? |
The amount of resistance - the steeper the gradient, the lower the resistance. |
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If a V-I graph has a curved line, what does this indicate? |
That the resistance is changing (the component is a non-ohmic conductor). |
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What is a diode? |
A special device made from a semiconductor material such as silicon. It lets current flow freely through it in one direction, but not in the other. |
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Why can't electricity flow in both directions in a diode? |
In the reverse direction there is a very high resistance, making it impossible for electricity to flow. |
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What is the use of a diode in a circuit? |
It's used to regulate the potential difference in circuits. |
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What is an LED? |
A light-emitting diode. It emits light when a current flows through it in the forward direction. |
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What do LEDs indicate? |
The presence of current in a circuit. |
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What are LEDs used for? Why? |
They are often used for lighting, as they use a much smaller current than other forms of lighting. They're often used in appliances to show that they're on and for the numbers on things like digital clocks, etc. |
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What is an LDR? |
A light-dependent resistor. It's a type of resistor that's dependent on the intensity of light. |
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In a bright light, what happens to the resistance of a light-dependent resistor? |
The resistance falls. |
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In darkness, what happens to the resistance of a light-dependent resistor? |
The resistance is highest. |
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What are light-dependent resistors used for? |
Things like automatic night lights, outdoor lighting and burglar detectors. |
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What is a thermistor? |
A thermistor is a temperature dependent resistor. |
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In hot conditions, what happens to the resistance of a thermistor? |
The resistance decreases. |
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In cool conditions, what happens to the resistance of a thermistor? |
The resistance increases. |
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What are thermistors used for? |
Thermistors make useful temperature detectors (like in a kettle or car engine). |
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In series circuits, how are the components connected? |
In a line, end to end, between the positive and negative of the power supply. |
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What type of circuit is this? |
A series circuit. |
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In a series circuit, what happens if you remove or disconnect one component? |
The circuit is broken and all components stop. |
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True or false: In a series circuit, potential difference is shared. |
True. The total potential difference of the supply is shared between the various components, so the voltage around in a series circuit always adds up to the source voltage. (V = V1 + V2 + V3...) |
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True or false: In a series circuit, the same current flows through all parts of the circuit. |
True. A1 = A2 |
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In a series circuit, what is the size of the current determined by? |
The total P.D. of the cells and the total resistance of the circuit. |
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In a series circuit, what is the total resistance the sum of? |
In a series circuit, the total resistance is the sum of all of the resistances: R = R1 + R2 + R3 |
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Complete this sentence: In a series circuit, the bigger the resistance of a component... |
...the bigger its share of the total potential difference. |
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True or false: In a series circuit, there is a bigger potential difference when more cells are in series, provided the cells are all connected the same way. |
True. For example, when two batteries of voltage 1.5V are connected in series, they supply 3V between them. |
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List three principles of a series circuit. |
1) The total resistance is the sum of the resistance of each component. 2) There is the same current through each component. 3) The total potential difference of the supply is shared between the components. |
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In a parallel circuit, how is each component connected to the power supply? |
Each component is connected separately to the positive and negative of the supply. |
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In a parallel circuit, what happens if you remove or disconnect a component? |
It will hardly affect the other components. |
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In a parallel circuit, how is potential difference shared? |
In parallel circuits, all components get the full source potential difference so the voltage is the same across all components. V1 = V2 = V3 |
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In a parallel circuit, if there are identical bulbs connected in parallel, how will their brightness compare? |
They will have the same brightness - the voltage is the same for both components. |
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State two principles of a parallel circuit. |
1) The potential difference across each component is the same. 2) The total current through the whole circuit is the sum of the currents through each component in the circuit. |
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In a parallel circuit, what happens if there's a 'branch'?
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The total current going into the branch equals the total current leaving - this current is shared between the components. |
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In a parallel circuit, what happens if two identical components are connected in parallel? |
The same current will flow through each component. |
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How are ammeters always connected? |
Ammeters are always connected in series, even if it's a parallel circuit.
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How are voltmeters always connected? |
Voltmeters are always connected in parallel with a component even in a series circuit. |
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Give a real life example of a series circuit. |
Christmas fairy lights are connect in series - the bulbs can be very small because the total 230V is shared between the bulbs so each bulb only has a small potential difference across it. |
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Everything electrical in a car is connected in parallel. Why? |
1) Everything can be turned on and off separately. 2) Everything always gets the full voltage from the battery. |
