Watts equal volts times amps. Watts measure how fast a load uses energy. They are a rate, like miles per hour.
The power card shows the same law three ways. Cover a letter in the triangle, and the two letters left show how to find it. A letter on top is divided by the one below. Letters side by side are multiplied.
Some books write E for volts and call the triangle "PIE".
Watt-hours count the total. Watt-hours equal watts times hours. 1,000 watt-hours make 1 kilowatt-hour (kWh). The power bill counts kilowatt-hours.
The clock runs sped up. The speed buttons change only the clock, so the amps and watts stay the same.
Each load runs nonstop here. A real heater's thermostat turns it on and off, so it uses less in a day.
Volts times amps equals watts for heaters and plain bulbs. Motors and electronics draw a little more current than this math gives. That is called power factor.
The watts come from each nameplate. Amps equal watts divided by volts. 60 ÷ 120 = 0.5 A. 1,500 ÷ 120 = 12.5 A. 1,500 ÷ 240 = 6.25 A. 4,500 ÷ 240 = 18.75 A.
Baseboard heaters come in 120 volt and 240 volt models with the same watts. Match the volts on the nameplate. Never put a 120 V heater on 240 V.
On 240 volts, both wires are hots. A two-wire cable has a black wire and a white wire. The white is taped red at both ends to mark it as a hot, per 200.8(C)(1). The heater does not use a neutral.
Both heaters count as continuous loads, per 424.5 and 422.13. A continuous load needs a breaker rated at least 125 percent of its amps, per 210.20(A).
The 120 volt heater draws 12.5 amps, so it needs at least 15.6 amps of breaker. It gets a 20 amp breaker and 12 AWG copper wire, per 240.4(D).
The water heater draws 18.75 amps, so it needs at least 23.4 amps of breaker. Most installers use a 30 amp breaker and 10 AWG copper wire, per 240.4(D).
The bulb and the 240 volt heater fit on a 15 amp breaker with 14 AWG copper wire.
Cable jacket colors show the wire size by maker custom, not by code. White is 14 AWG, yellow is 12 AWG, and orange is 10 AWG.
120 V and 240 V are nominal system voltages. Load calculations use them, per 120.5(A). A real meter reading runs a little above or below.
The dots show how much current flows. More dots passing each second means more amps. The dots do not show how fast electrons move. Real electrons drift far slower than a snail, a fraction of a millimeter per second in house wiring.
Wall power is AC. It runs 60 cycles a second, so it reverses 120 times a second. That is too fast to see. The dots show how much current flows, out on one wire and back on the other.
The warm glow on an element shows watts turned into heat. A real element in water does not glow.
A water heater element must sit in water. In air it burns out. That is why it is drawn inside its tank.
The panel, breaker, and ground wire are left out of the picture. A real heater's metal case is grounded. Always test before you touch. That is standard trade practice.
Reading volts on a live circuit is a trained task. Use a meter rated for the job and the right insulated gloves.