Electrical resistance facts for kids

Imagine electricity flowing like water through a pipe. Electrical resistance is how much that pipe makes it hard for the electricity to flow. It shows how voltage (the push of electricity) and current (the amount of electricity flowing) are connected. If there's more resistance, less electricity can get through a circuit. Almost everything has some resistance, except for special materials called superconductors.

What is Ohm's Law?

A scientist named Georg Simon Ohm discovered resistance in 1827. He found that resistance is basically the relationship between voltage and current. He created Ohm's law, which says that if the temperature stays the same, the voltage between two points in a conductor changes directly with the current.

He described this with a simple math equation:

This equation helps us understand the relationship, where:

• is the resistance of the object. We measure it in ohms (Ω).
• is the voltage across the object. We measure it in volts (V).
• is the current flowing through the object. We measure it in amperes (A).

How to Calculate Resistance

Think of a road for cars. A long, narrow road makes it harder for many cars to pass. But a short, wide road lets more cars through easily. It's similar with wires and electricity. A long, thin wire has more resistance than a short, thick one.

We can calculate the resistance () of a wire that has the same width all the way through using this formula:

In this formula:

• is the length of the wire. We measure it in meters (m).
• is the cross-sectional area of the wire. This is like the size of the wire's cut end. We measure it in square meters (m²).
• Failed to parse (Missing <code>texvc</code> executable. Please see math/README to configure.): ρ (which is the Greek letter rho) is the electrical resistivity of the material. This number tells us how much a specific material naturally resists electricity. We measure it in ohm-meters (Ω m).

Example Calculation

Let's find the resistance of a copper wire.

• The wire has a radius of 2 millimeters (mm).
• Its length is 5 meters (m).

Here's how we solve it:

• The resistivity () of copper is Failed to parse (Missing <code>texvc</code> executable. Please see math/README to configure.): 1.68 \times 10^{-8} \, Ω m.
• First, we find the cross-sectional area (). Since the radius is 2 mm, which is Failed to parse (Missing <code>texvc</code> executable. Please see math/README to configure.): 2 \times 10^{-3} meters, the area is Failed to parse (Missing <code>texvc</code> executable. Please see math/README to configure.): \pi r^2 = \pi \times (2 \times 10^{-3})^2 = 4\pi \times 10^{-6}\, square meters.
• The length () is meters.

Now, we use the formula : Failed to parse (Missing <code>texvc</code> executable. Please see math/README to configure.): R = 1.68 \times 10^{-8} \frac{5}{4\pi \times 10^{-6}} \approx 6.685 \times 10^{-3}\Omega \, So, the resistance of this copper wire is about 0.006685 ohms.

Where is Resistance Used?

Resistors come in many shapes and sizes.

Resistors are special parts used in electrical circuits. Their main job is to provide a specific amount of electrical resistance. This helps control the flow of electricity in a circuit. For example, resistors can make sure that a light bulb gets the right amount of current so it doesn't burn out. They are very important in almost all electronic devices we use every day.

Images for kids

• 

  A 75 Ω resistor, identified by its electronic color code. An ohmmeter could check this value.

• 

  A piece of resistive material with electrical contacts on both ends.

• 

  An ohmmeter, a device used to measure resistance.

• 

  When current flows through a material with resistance, it creates heat. This is called Joule heating. Here, a cartridge heater is glowing red hot because of this effect.

See also

In Spanish: Resistencia eléctrica para niños