Final answer:
The proper fuse size for a 240-volt, 15,000-watt furnace is 65 amperes. When multiple devices like a toaster, frying pan, and lamp, drawing a combined current of 27.295 A, are plugged into a circuit with a 15-A fuse, the fuse will blow.
Step-by-step explanation:
Calculating Fuse Size for a Furnace
To determine the standard size fuses required for a 240-volt, 15,000-watt furnace, we use the formula P=IV, where P is power in watts, I is current in amperes, and V is voltage. Rearranging the formula to solve for I gives us I = P/V. Substituting 15,000 watts for P and 240 volts for V gives us I = 15,000/240, which equals 62.5 amperes. Since fuses are typically rated in standard sizes, we would choose the next highest standard size, which would be 65 amperes, as the correct answer.
Analysis of Multiple Devices on a Single Fuse
When an 1800-W toaster, a 1400-W electric frying pan, and a 75-W lamp are plugged into the same 120-V circuit, we calculate the current drawn by each device. For the toaster, I = 1800W/120V = 15A; for the electric frying pan, I = 1400W/120V = 11.67A; and for the lamp, I = 75W/120V = 0.625A. Adding these currents together, we get 27.295A, which is greater than the 15A fuse's rating, therefore, this combination will blow the 15-A fuse.