Antique Radios | Volts, Amps, Watts & Ohm’s Law

To help explain how electricity flows through a wire, the analogy of water flowing through a pipe is often used. I’m a bike rider, though, so I think of it more as a cyclist riding down the road. It’s actually pretty simple.

A bicycle rider has stored energy which can be used to turn a bike wheel.
A battery has stored energy which can be used to turn ON an electrical device, such as a bulb.

By applying pressure to pedals, which is measured in torque, there is potential for energy to be delivered through the chain.
By applying pressure to electrons, which is measured in volts, there is potential for energy to be delivered through wires.

The rate that a rider moves a specific amount of chain, is measured in revolutions per minute or RPM.
The rate that a battery moves a specific amount charge through wires, is measured in amps.

The combined power of torque and RPM to turn a wheel is measured in watts.
The combined power of volts and amps to electrify a device like a bulb... Is also measured in watts.

If a rider encounters a headwind on the ride, the same amount power will no longer deliver the same amount of wheel speed. Wind resistance is measured as a coefficient of drag.

If a battery encounters increased resistance when powering a bulb, the same amount of power will no longer deliver the same amount of brightness. Electrical resistance is measured in ohms and is represented by the omega symbol.

If a rider is to move the wheel at the same rate with increased headwind, as without... The pressure applied to the pedals needs to increase. This can only happen, though If the rider has the required strength and stamina.

If a battery is to power a bulb at the same brightness with increased resistance as without, the electrical pressure, or volts needs to increase. This can only happen, though, if the power source can provide the necessary volts, at the required amps.

Ohm’s Law & Other Rules of The Road

Just as math formulas can be used to analyze a bike rider’s work... There are formulas to analyze electricity’s work.

A bike rider’s watts, for example equals torque, times RPM.

Electrical watts, equals volts times amps.

To calculate ohms, volts and and amps, we use Ohm’s law. Ohm’s law states that Volts equals ohms times amps. So, ten ohms, and ten amps equals 100 volts.

The formula can be rearranged, stating that Ohms equals volts divided by amps. Or that amps equals volts divided by ohms.

And since watts equals volts times amps, 100 volts at 10 amps equals 1,000 watts.

To see how useful this can be, let’s solve an electrical problem.

This battery provides 9 volts.

This bulb, requires 6.3 volts at .15 amps, making it a .945 watt bulb.

If we connect the 9 volt battery to the bulb, it will run too hot and blow.

That’s because the .15 amps drawn from the bulb, at the battery’s 9 volts, produces 1.35 watts, and the bulb is only able to handle .945 watts, at 6.3 volts.

If we want to use this battery with this bulb we need to remove 2.7 volts, and .405 watts. We can do this by adding a resistor. A resistor is an electrical component that creates resistance. As we learned, resistance is measure in ohms.

To calculate how many ohms of resistance is needed, we turn to Ohm’s law, which again, states that ohms equals volts divided amps. So, if we take the 2.7 volts we need to drop, and divide it by the .15 amps the bulb draws, we find that we need to add 18 ohms of resistance.

And that’s just what an 18 ohm resistor does. So let’s connect the battery and bulb now with the resistor in-between. Perfect. And that’s how Ohm’s law... Solves problems.

But wait a second, how do we know this is an 18 ohm resistor? Because the bands say so. We’ll learn more about them and more in the next video. To stay updated, please subscribe and click the bell. And if you like this video, give it a thumbs up. See you soon.

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