SP13 Word Scramble
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| Question | Answer |
| What does a changing magnetic field around a wire cause? | It induces a potential difference. |
| What flows then there is a potential difference? | A current . |
| What does the size of the induced potential difference in a coil dependent on? | How fast the magnetic field is changing or moves past the coil |
| What happens to the induced p.d. if the magnetic field is reversed? | The direction of the p.d. reverses |
| What does a generator consist of? | A coil that is rotated in a magnetic field |
| What are the ends of the coil connected to? | Slip rings. |
| What touches the slip rings so they are connected to the external circuit? | Carbon brushes. |
| What type of current is produced by a coil rotating with slip rings in a magnetic field? | Alternating current. |
| If the ring is connected to a commutator, what type of current does it generate? | Direct current. |
| What is the name of a generator that produces direct current? | Dynamo. |
| What is the national grid ? | This is system of wires and cables that bring electricity from the power system to our homes and other buildings. |
| Where is energy lost in the national grid? | By heating of the transmission lines. |
| What happens if the voltage (potential difference ) across the transmission wire is increased? | The current decreases. |
| Why do we transmit electricity at low currents? | Less energy is dissipated at heat to the surrounding air and it is more efficient. |
| What type of transformer increases the voltage (potential difference) as the electricity leaves the power station? | A step up transformer. |
| What voltage ( potential difference change is there by the step up transformer? | 25kW to 400kW |
| What type of transformer reduces the voltage (potential difference before it enters our homes? | A step down transformer. |
| What happens to the current as electricity passes through a step down transformer? | It increases. |
| What are the two coils in a transformer called? | primary and secondary. |
| If the voltage (potential difference ) is to be increased what can you state about the ratio of the coils in the transformer? | There are more coils on the secondary compared to the primary. |
| What is potential difference? | It is a measure of the energy transferred by each coulomb of charge that flows through a wire. |
| What does the current measure? | It measures the number of coulombs per second passing a point in a circuit. |
| What is electrical power? | It is the energy transferred by the electric current each second. |
| What is the equation for electrical power? | Electrical power = current x potential difference |
| What is the equation in symbols? | P = I X V |
| What is the principle of conservation of energy? | Energy cannot be created or destroyed only transformed into other forms. |
| What can you say about the power supplied by the primary coil compared to the power transferred away from the secondary coil? | They are the same. |
| How can this be written in an equation in symbols? | Vpx Ip = VsxIs |
| What is assumed in the transformer equation? | It is assumed that the transformer is 100% efficient and there are no energy losses. |
| If Ip=2A, Vs=200V and Is=0.1A, what is Vp? | "Vpx Ip = VsxIs Vp x 2= 200 x 0.1 Vp x 2= 20 Vp =20/2=10V |
| Current which regularly changes direction is called… | alternating current |
| An example of alternating current is…? | mains electricity |
| Current which flows in one direction is…? | direct current |
| An example of direct current is… | batteries |
| What is the potential difference of mains electricity in the UK? | 230V |
| What is the frequency of the alternating current in UK mains electricity? | 50Hz |
| The national grid consists of…? | Cables and transformers |
| Are power stations par of the national grid? | no |
| What does a step up transformer do? | Increases p.d. |
| What does a step down transformer do? | reduces p.d. to 230 V |
| Why are transformers used? | reduce current so that less heat is lost in cables, increases efficiency |
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Davenant Foundation School
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