11144697
Description
Flashcards by Natalia Cliff, updated more than 1 year ago
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Created by Natalia Cliff
over 7 years ago
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| Question | Answer |
| What is Electric Current? | The rate of flow of charged particles I=Q/t |
| What is the charge of an electron? | 1.6 x 10^-19 This can also be used to calculate the charge of an ion |
| What Direction does Current flow? | -Conventional Current travels from positive to negative -The electrons actually move from negative to positive |
| What is Potential Difference? | Potential Difference is a measure of the energy provided to a component per unit of charge. V=E/Q |
| What is the EMF of a Circuit? | -Electromotive Force -the work done by a battery per unit of charge. (essentially the potential difference of the battery) |
| What is an Electronvolt? | -An electronvolt is a unit of energy used for subatomic particles -It comes from V=E/Q when Q is 1.6 x 10^-19 -Therefore, one electronvolt is 1.6 x 10^-19 J |
| What does Ohm's Law state? | -The current in an ohmic conductor is directly proportional to the potential difference across it, provided that temperature and other physical factors are kept constant -V=IR, but ONLY in ohmic conductors |
| How does Increasing Temperature affect Resistance? | As temperature increases, the metal's lattices vibrate more and so the electrons bump into them more often, thereby increasing resistance |
| Why do we use Resistivity? | -Resistance doesn't take the length or cross sectional area of a wire, and so varies with different wires of the same metal -So instead we use resistivity |
| What is Resistivity? | -A measure of how much a material opposes the flow of charge -\[\rho\]=RA/l It's divided by a lowercase L -The units are ohm meters |
| Why is Resistivity Quoted at a Specific Temperature? | -Resistivity is dependent on resistance, which changes with temperature. -Therefore resistivity also changes with temperature |
| What are Semiconductors? | Materials that act as insulators at absolute 0, but can sometimes conduct electricity |
| How can Semiconductors Conduct? | -In solids, because atoms are packed so closely together, they form energy bands rather than levels. -The band of outermost electrons is called the valence band -If the electron is provided with enough energy, it can jump over the energy gap into the conduction band where it is free to move and so can carry charge |
| How do the Valence and Conduction Bands Interact in Conductors and Insulators? | -In metals, the valence and conduction band overlap -In insulators the energy gap is too large, the material is damaged before electrons have enough energy to move into the conduction band |
| What is a "Hole"? | When an electron moves from the valence band to the conduction band, it leaves behind a hole in the valence band, which acts as a positive charge carrier |
| Why does Resistance Decrease as Temperature Increases in a Thermistor? | In a Negative Temperature Coefficient Thermistor: -Even though the more vibrations in the metal lattice increase resistance -This is outweighed by the fact that the thermal energy causes electrons in the semiconductor to move from the valence band to the conduction band -This allows more current to flow through the semiconductor, thereby reducing the resistance |
| What reduces the resistance in an LDR? | -Resistance in an LDR reduces with Light Intensity -Because the light energy causes electrons to move from the valence band to the conduction band -This means that a larger current can flow as there are more charge carriers free to move -So there is a smaller resistance |
| How do Semiconductor Diodes work? | -Semiconductor Diodes are made by joining different kinds of semiconductors. -This creates an energy barrier that can be overcome by a small forwards p.d. (0.6v in silicon) but needs a very large reverse p.d. to overcome -Only a very tiny leakage current makes it out in the reverse direction |
| How can you make a Superconductor? | -Resistance in a metal decreases as temperature decreases -If you cool a metal beneath it's critical temperature, it has 0 resistance and is a superconductor |
| Why are Superconductors used? | Superconductors are used because when a large current is needed, a normal conductor would waste a lot of energy and damage it's surroundings due to the heat energy dissapated |
| What is Drift Velocity? | Drift Velocity is the slow net movement of electrons I=nAVe |
| Current in Circuits | Kirchhoff's first law - the sum of current leaving any junction is always equal to the sum of the current that entered it -This is due to the CONSERVATION ON CHARGE -So current is added in parallel and the same in series |
| P.d. in Circuits | Kirchhoff's second law - the total voltage across a circuit loop is equal to the sum of the voltage drops across components -This is due to the CONSERVATION OF ENERGY and V=E/Q -So P.d. is the same in parallel and added in series |
| Resistance in Series Equation | |
| Resistance in Series Derivation | |
| Resistance in Parallel Equation | |
| Resistance in Parallel Derivation | |
| V I Graph for a Filament Lamp | |
| V I Graph for Ohmic Conductor | |
| V I Graph for Semiconductor Diode | |
| V I Graph for Thermistor | |
| How does P.d. Vary Along a Wire? | Along a uniform, current-carrying wire, the longer it is, the larger the resistance, so the potential difference also increases. |
| What is a Potential Divider Circuit? | -In a series circuit, the p.d. is split in proportion to the resistance of the components. -This allows one to chose a specific voltage across a component and it's parallel branch. -This creates a potential divider circuit |
| What is the Equation used for a Potential Divider Circuit? | V(out) = V(in) x R(2) / (R(1) + R(2)) |
| What happens when a potential Divider Circuit has a Sensor Component in it? | -If one of the resistors is sensor component such as a LDR or Thermistor, this resistance will vary. -This can be used to control external circuits by placing these in parallel with the sensor component |
| What is Internal Resistance? | The resistance of a battery |
| How does the Internal Resistance Affect the Circuit? | -The internal resistance means that the emf can't supply it's maximum potential difference. -This p.d. that never makes it to the circuit is referred to as lost volts -The emf minus the lost volts leaves us with the terminal p.d. of the circuit -When r is internal resistance, and R is resistance in the Circuit, EMF = V + Ir |
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