Resistance & Current 2

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Measuring Resistance

We calculate the resistance using R = V/I. We calculate potential difference using a voltmeter and current using an ammeter at the same time.

Potential difference across a component

To measure the resistance of a component (e.g. lamp or resistor), measure the potential difference across the component.

Current through a component

Use an ammeter to measure the current flowing through a component.

Resistance

The longer the wire, the higher the resistance

In series circuits, the resistors all oppose the flow of electric current through the circuit. Their total resistance is calculated by adding up the resistances of each individual resistor: R = R1 + R2 + R3 +....

Water pipes

If you take a single pipe with water (like electric current) flowing through it, and put a rock into it, the rock blocks the flow of water (like a resistor).
Adding more rocks next to each other in the pipe makes it harder to push water through.

Resistance

The combined resistance of two resistors in parallel is less than the resistances of either of the two resistors by themselves.

Like water draining through a bucket

Consider a bucket full of water with a hole in the bottom:
- Water drains out of the bucket.
- If a second hole is drilled into the bucket the water (like adding another resistor in parallel) will drain faster.
- It does not matter how narrow the second hole is (how high it’s resistance is), it is always faster for water to flow through two holes instead of one.