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| Pregunta | Respuesta |
| What is the definition of electric charge? | A fundamental property of matter - all electrons and protons are charged, and if an atom loses or gains electrons, it can become positively or negatively charged. |
| How does rubbing a plastic rod with a cloth make it charged? | The electrons shift balance - either some electrons go from the cloth to the rod, or from the rod to the cloth. Either way this makes them positively and negatively charged. |
| What is the definition of an electric field? | A region where an electric field experiences a force. |
| What is electric current, in four words? | A flow of charge. |
| Charges don't move very quickly - so how come a bulb switches on immediately when a circuit is connected? | There are masses of amounts of charges in every component, and they all move together when given energy by a power source. |
| How does a battery work? | The chemicals in the battery make positive charges connect at one terminal and negative charges at another. |
| In which direction does conventional current go and in which direction do electrons flow? Why does this matter? | Conventional current is positive to negative, whilst electrons go negative to positive. But actually this doesn't matter! Electron flow is 'right' but conventional current is the most used. |
| What happens to a bulb when a current increases? | The bulb will grow brighter and brighter, unless the current gets so strong it 'blows'. |
| What is used to measure current? | An ammeter. |
| In a series current, what would roughly happen to a current of 10A after it's past through a bulb? | It would stay 10A - current in a series circuit is the same everywhere. |
| What two advantages are there of circuits in parallel? | If one component breaks the rest of the circuit will still work, and component can be switched on and off independently. |
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a = 50A, b = 100A, d = 150A |
| What happens to a bulb when a current increases and why? | The bulb will grow brighter and brighter until it blows - but not because the voltage makes it blow, because the higher the voltage the higher the current. |
| How does a bulb use resistance to work? | The filament of a bulb has lots of resistance due to the structure of the metal not easily allowing electrons to move through them. Lots of energy is used up getting past the filament, which is emitted as light energy. |
| When resistance increases, what happens to current? | decreases |
| What rule means 'the current through a resistor is proportional to the voltage'? | Ohm's law |
| Name two variable resistors and explain how they work. | An LDR or light-dependent resistor has higher resistance when it's dark. A thermistor almost always has higher resistance when it's cold. |
| What happens to the total resistance when a resistor is added to a simple circuit in parallel or in series? | In series the total resistance is larger, but in parallel it's actually smaller. |
| What is the definition of voltage? | A measure of the 'push' it exerts on a charge in an electric circuit. |
| What is potential difference? | The difference in potential energy between any two points in an electric circuit. |
| What is the potential difference for resistors in a parallel and in a series circuit? | In a parallel circuit the potential difference is the same for every resistor and equal to the battery voltage, and in a series circuit the sum of every resistor is equal to the battery voltage. |
| In a series circuit, which would have the bigger potential difference, a small or a large resistor? | A large resistor. |
| How does potential difference have a use in circuits? Describe. | Potential dividers, as they're called, allow voltage to be varied. If a variable resistor lowers it's resistance it'll have a lower p.d. and therefore another resistor in series will have a bigger voltage. |
| What is 'power' in electric circuits and how is it worked out, with units? | Power is the rate at which work is done by the power supply (aka battery) on the components of the circuit. Power (watt, W) = current (ampere, A) x voltage (volt, V). |
| What is one watt equal to in energy terms? | One joule per second. |
| There's a link between electricity and magnetism. Describe this link, without an explanation. | When there's an electric current in a wire there's a magnetic field in the region around the wire. |
| A square wire is placed between a north and a south magnet. When a current is passed through it, what happens and why? | The square magnet rotates at the sides by 90 degrees. This is because the magnetic push is at right angles to the electric current (aka the wire) and the magnetic field lines at the sides. One force is up, the other down, which makes the wire turn. |
| What makes the wire turn more than 90 degrees? | Brushes rub against a split ring commutator that makes the current reverse twice every turn, so the coil keeps rotating. |
| What is the name of the process in which a potential difference is generated in a wire when it's in a changing electromagnetic field? | electromagnetic induction |
| What does it mean that potential difference is generated in a wire during electromagnetic induction and how? | Potential difference is voltage, and if the circuit is complete this means current is also generated. It occurs because when a magnetic is moved in or out of coil, the magnetic field lines are 'cutting' the coil. |
| In what four ways can the induced voltage produced be increased? | Move the magnet in and out faster, use a stronger magnet, put an iron core in the wire or use a coil with more turns. |
| Describe alternating current and direct current. | a.c. is an electric current that reverses many times a second whilst d.c. is an electric current that stays in the same direction. |
| What is a transformer, how does it work and what's it used for? | An electrical device consisting of two coils of wire wrapped around an iron core. An alternating current in one coil causes an ever changing magnetic field that induces an a.c. current in the second coil. This is used to step up or down voltages in the National Grid. |
| Why is the voltage stepped up and later stepped down in the National Grid? | It's stepped up because when the voltage is high the current is small, which is what wastes energy, and it's stepped down so it can be used in the home. |
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