We carried out the following investigation: 2) a) The current flowing in a series circuit is the same wherever we measure it. That is, the current flowing into a component is equal to the current flowing out of that component b) the current will decrease as we add more bulbs in series (and the bulbs will become dimmer) c) The current splits in a parallel circuit. The sum of the current in each of the branches will add up to the current flowing from the power supply 3) When a bulb is added in parallel we should expect a) the bulb brightness to stay the same (there might be a slight dimming in practice because of internal resistance in the battery - to be covered in section (surprisingly) on internal resistance) b) the current at G should stay the same (since the bulb brightness stays the same) c) The current at F will therefore have to increase Kirchhoff's 1st Law The sum of the currents flowing into any point is equal to the sum of the currents flowing out of that point. This law is a consequence of the law of conservation of charge This is evident from out empirical observations from the circuits above and summarised below: Mean Drift Velocity
Free (or disassociated) electrons in a metal are the electrons that move throughout the metal. When no voltage is applied across the metal the electrons show random thermal behaviour. All of the free electrons are moving randomly and so the resultant current is zero. However, when a voltage is applied across the ends of the metal the electrons will drift in the direction from the negative side of the power source to the negative side. The mean drift velocity is the average speed these electrons show in drifting through the metal. A derivation for the drift velocity, v, for electrons in a metal (in terms of current, I, charge, q, charge carrier density, n, and cross-sectional area, A) is shown below: |
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