A 1250 W radiant heater is constructed to operate at 115 V. (a) What is the current in the heater when the unit is operating? (b) What is the resistance of the heating coil? (c) How much thermal energy is produced in 1.0 h?

A fuse in an electric circuit is a wire that is designed to melt, and thereby open the circuit, if the current exceeds a predetermined value. Suppose that the material to be used in a fuse melts when the current density rises to $\mathbf{440}\mathbf{}\mathit{A}\mathbf{/}\mathit{c}{\mathit{m}}^{\mathbf{2}}$. What diameter of cylindrical wire should be used to make a fuse that will limit the current to 0.50 A?

A block in the shape of a rectangular solid has a cross-sectional area of 3.50cm² across its width, a front-to-rear length of 15.8cm , and a resistance of $\mathbf{935}\mathbf{\Omega }$. The block’s material contains $\mathbf{5}\mathbf{.}\mathbf{33}\mathbf{\times }{\mathbf{10}}^{\mathbf{22}}$ conduction electrons/m³. A potential difference of 35.8 V is maintained between its front and rear faces. (a) What is the current in the block? (b) If the current density is uniform, what is its magnitude? What are (c) the drift velocity of the conduction electrons and (d) the magnitude of the electric field in the block?

A cylindrical metal rod is 1.60 m long and 5.50 m in diameter. The resistance between its two ends (at $\mathbf{20}\mathbf{°}$) is $\mathbf{1}\mathbf{.}\mathbf{09}\mathbf{\times }{\mathbf{10}}^{\mathbf{-}\mathbf{3}}\mathit{\Omega }$ . (a) What is the material? (b) A round disk, 2.00 cm in diameter and 1.00 mm thick, is formed of the same material. What is the resistance between the round faces, assuming that each face is an equi-potential surface?

Near Earth, the density of protons in the solar wind (a stream of particles from the Sun) is $\mathbf{8}\mathbf{.}\mathbf{70}\mathbf{}\mathit{c}{\mathit{m}}^{\mathbf{-}\mathbf{3}}$ , and their speed is 470 km/s . (a) Find the current density of these protons. (b) If Earth’s magnetic field did not deflect the protons, what total current would Earth receive?

The headlights of a moving car require about 10 A from the 12 V alternator, which is driven by the engine. Assume the alternator is efficient (its output electrical power is 80% of its input mechanical power), and calculate the horsepower the engine must supply to run the lights.