Please help: A four slice toaster is rated at 1200W and designed for use with 120V circuits.?

Question

Could someone please help me with this I am really lost :(


a) what is the resistance of the toaster
b) How much current will flow when the toaster is on
c) What is the power of the toaster?
d) If it takes 3 minutes to properly make toast, and the cost per kilowatt-hour is 10 cents, how much does it cost to make one slice of toast?

Answer 1

Ohm's law E= I * R
Watts = E * I
1200 = 120 * I
10 = I

a) R = E / I
= 120 /10 = 12 ohms.
b) 10 amps.
c) 1200 watts.
d) One or four slices makes little difference.
Three minutes is 1/20'th of an hour
Because the toaster costs 12 cents per hour to operate it would be:
12/20
=3/5 cent
=$0.006

Answer 2

V X I = Power and we have 120 X I = 1200 and so I = 10 amps and we have Resistance R = V / I = 120 / 10 = 12 Ohms (assuming that the power factor is 1)

We have already calculated the current I = 10 amperes

The power of the toaster is its wattage and is 1200 W

Power consumed in three minutes is 1200 / 20 = 60 watts and the cost is 12/20 = 0.6 cents

Answer 3

c) is the easiest to answer: 1200W, the power of the toaster
Then b) P= I x V, so I = P/V or 1200/120 which is 10 A.

a) is now possible, R = V/I or 120/10 or 12 ohms.

d) involves a lot of arithmetic. It will start you off to know that 1 kW h is 1000W x 3600 seconds or 3 600 000joules.
3 minutes is 3 x 60 or 180 seconds.
Then figure out the energy needed to toast 4 slices using W = P x t; set that as a fraction of 3 600 000 joules (1 kW h); multiply by 10 cents; divide by 4 slices.
Good luck!

Answer 4

b) P = VI, so 1200 Watts = 120 V * I => I = 10Amps
a) V = IR, so 120 V = 10Amps * R => R = 12 ohms
c) P = 1200Watts (given)
d) 1.2 kW * 1/20 hour * $0.10 = $0.006

Edit: After seeing another answer, note that, for the last part, that cost is the same to make a single slice, or all four slices at once, so you could also say the per-slice cost is 1/4 of that, if you make them in batches of 4.