Units for voltage, current and resistance

Hmmm … two deciliteres of sugar, five deciliteres of flour, a hundred grams of butter, bake for 30 minutes at 200 degrees … Decilitres, grams, minutes and how many degrees Celsius ... are examples of things that, in physics, are called units. … and then there's one egg, too … Hold on, Philip! That shouldn't go in the cake mix, should it!? Just like with volume, temperature and time, you can measure and give values to current, voltage and resistance in an electric circuit too. Voltage - this is a measure of how large the "urge" that electrons have to move from one place to another is.

It is measured in Volts. An ordinary flashlight battery usually has a voltage of 1.5 Volts, but there are batteries with other voltages. The voltage in a wall socket is 230 Volts, which is more than 150 times higher than the battery in Philips hand. The voltage in the live cables for a train are 25 thousand Volts. More than 100 times higher than in the wall socket.

If voltage that high were to pass through your body, you would be badly injured, often fatally. The voltage is so high that the current can travel several decimeters through the air. Which is why it's important never to go near a broken high-voltage cable. So what happens when the battery's poles are connected? Well, since the electrons urgently "want" to get to the other side, they begin to move through Philip's hand.

The body has a low conductivity, so it's a very small current that passes through his hand. Current is a measure of how much charge passes every second. Current is measured in the unit Ampere. How many electrons pass every second if the current is one Amp? Six billion-billion.

That’s about as many electrons as there are insects in the World. In order to get a current as high as one Amp from an ordinary flashlight battery ... the current needs to pass through something with lower resistance - like a copper wire. But! If you short-circuit a battery like this, it will discharge quickly.

The higher the voltage: the more Amperes - or ‘Amps’ - will pass through the circuit. In order to raise or lower the current without needing to change the voltage of the supply, you can change how much resistance there is in the circuit. Resistance is measured in Ohms. It’s written with the Greek letter Omega. When you make calculations with current, voltage and resistance, you use these units.

For example: If you have a resistance of 5 Ohms and a voltage of 9 Volts, you find the current by dividing the voltage of 9 Volts by the resistance of 5 Ohms. In this case, the current is then 1.8 Amps. But go on, Philip. Finish the cake now, so you can think about these units later … But remember this! Voltage is measured in Volts, and shows the strength of the electrons’ urge to move through the circuit.

Current is measured in Amperes, and measures how much charge passes through the circuit. The thing that hinders the current, electrical resistance, is measured in Ohms.