Q&A: ‘Watts’ vs ‘volts’ vs ‘amps’ vs ‘ohms’

Each week here at the Australian Writers’ Centre, we dissect and discuss, contort and retort, ask and gasp at the English language and all its rules, regulations and ridiculousness. It’s a celebration of language, masquerading as a passive-aggressive whinge about words and weirdness. This week, the powers that be…

Q: Hi AWC, can we talk about power?

A: Power tools, power naps or power dressing?

Q: None of them – rather the units we measure electricity with. I can never figure out the difference between volts and watts and amps etc.

A: Oooooh, that’s a good one – and you’re not alone in finding it confusing. There are a lot of people who struggle with units.

Q: Shall we start with volts?

A: Sure. It’s named after Alessandro Volta – the Italian physicist who invented the electric battery in 1800. A volt is the standard unit of voltage. The Macquarie Dictionary defines “voltage” as “electromotive force”.  

Q: Huh?

A: It’s the difference in electric potential between two points in an electric circuit. Think of it like the pressure that pushes the current through in order to power something. Households in Australia get electricity at 220-240V, while America is typically half this. 

Q: What about power lines?

A: Those carry a LOT more electricity – up to 400,000 volts!

Q: How does it transform the high voltage to house levels?

A: You just said it. Via a “transformer”!

Q: Optimus Prime?

A: No, not the robots in disguise.

Q: Okay, so you mentioned current?

A: Yeah, so if voltage (measured in volts) is the pressure that pushes the current, the current is the actual flow of electrons. The rate of flow is measured in “amperes”.

Q: Is that the same as “amps”?

A: Yeah, it’s often shortened to that. Same thing.

Q: And an electric guitar amp?

A: No, that “amp” is short for “amplifier”. Different thing.

Q: But what if the guitar is being played by a member of AC/DC?

A: Haha, okay, we see what you did there. AC/DC does indeed stand for “alternating current/direct current” – two different ways that electricity flows through a conductor. Things like batteries are DC while your home’s electricity is AC.

Q: So the 240V coming into my house is pushing an alternating current and measured in amperes?

A: Well, for your house, a more useful measure is “hertz” – the rate of change in the directional flow of electricity. One hertz is equal to one wave of alternating current (also called a “cycle”) per second. Australia's residential power supply is 240V, 50Hz. 

Q: So, back on amps – it’s a measure of the amount of electric charge?

A: Well, technically, another unit called a “coulomb” measures the charge itself, while an “ampere” is the FLOW of the charge. 

Q: Wow, that’s splitting amp-hairs.

A: Haha, maybe, but it’s an important distinction. By the way, amps are named after French mathematician and physicist André-Marie Ampère. Meanwhile, Charles-Augustin de Coulomb was another Frenchman.

Q: Okay, what’s next?

A: No, not watts.

Q: Huh?

A: Never mind. Next, it’s worth discussing “ohms”.

Q: There’s no place like “ohm”!

A: Named after German scientist Georg Simon Ohm, the “ohm” is the resistance of a conductor in which one volt produces a current of one ampere.

Q: Huh?

A: Think of it as a measure of how well a current can travel through a circuit.

Q: So it’s the resistance to an electric current?

A: Yep. So, let’s stocktake. Vocabulary dot com equates it to water flowing through a pipe.  The water pressure is the voltage (volts), the rate at which it flows is the current (amps), and the SIZE of the pipe is the resistance (ohms).

Q: Nice! So, now surely we need to talk about “watts”, yeah?

A: Okay. So far we’ve been supplying electricity into a house or an appliance.  “Watts” measure the output – the product of voltage and current. Named after Scottish scientist James Watt.

Q: So a watt measures how effective the electricity is?

A: Yeah, the useful work an appliance does is measured in watts. You literally multiply the voltage by the current. So a 2400W heater is calculated by 10 Amps of current at 240 Volts.

Q: So my energy bill is calculated in this way?

A: Almost! For that, you need to remember that a “watt” (often kilowatts or kW) measures power – the rate at which something uses electricity. However, the amount of electricity used over time is measured in kilowatt hours – or kWh.

Q: Ah okay, so “power” is measured in watts, but “energy” is watts used over time?

A: Correct. The longer you have your heater on, the higher your energy bill.

Q: Well, this has been a highly charged discussion.

A: Yes, plenty of “current” events!

Q: This kind of reminds me of my woollen jumper that I had to return to the shop as it was giving me static electricity shocks.

A: Really? Did they replace it?

Q: Yes, free of charge! Bahahaha.

A: Ugh. Go ohm…

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