# Exp8Physics

**Topics:**Electrical resistance, Resistor, Hard water

**Pages:**2 (698 words)

**Published:**November 20, 2014

1. What are the laws of series resistors? Of parallel resistors? Are these laws verified in your experiment?

Ohm’s Law - Ohm's law states that the voltage (V) across a resistor is proportional to the current (I), where the constant of proportionality is the resistance (R). Series and parallel resistors - The total resistance of resistors connected in series is the sum of their individual resistance values. The total resistance of resistors connected in parallel is the reciprocal of the sum of the reciprocals of the individual resistors. Power dissipation - where V (volts) is the voltage across the resistor and I (amps) is the current flowing through it. Using Ohm's law, the two other forms can be derived. This power is converted into heat which must be dissipated by the resistor's package before its temperature rises excessively.

2. You have 4 identical resistors, each with a resistance of 5 ohms. Show all possible values of resistance that you can get using all four resistors. all in series, 20 Ω

all in parallel, 5/4 ohm = 1.25 Ω

3 in parallel, 1 in series, 5/3 + 5 = 6.67 Ω

2 in parallel, 2 in series, 5/2 + 5•2 = 12.5 Ω

2 strings of 2, strings in parallel. 2*5/2 = 5 Ω

two parallel pairs, in series, 2*5/2 = 5 Ω

1 string of 3, 1, in parallel, 15 || 5 = 1 / [ (1/5) + (1/15) ] = 3.75 Ω

3. As more doors are opened in a crowded room, the resistance to motion of people trying to leave the room is reduced. How is this similar to what happens when more branches are added to a parallel circuit?

The more branches you add to a parallel circuit (the more things you plug in) the lower the total resistance becomes. Remember that as the total resistance decreases, the total current increases. So, the more things you plug in, the more current has to flow through the wiring in the wall.

4. Are household circuits normally wired in series or in parallel? Why?

Parallel. In parallel, all devices get the same...

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