(II) A 100-W lightbulb has a resistance of about 12 Q when cold (20°C) and 140 N when on (hot). Estimate the tem- perature of the filament when hot assuming an average temperature coefficient of resistivity a = 0.0045 (C°)-1.

(b) A voltage of 3 V is applied across the ends of a copper alloy conductor which has a resistance of 1.5 at room temperature (20 °C). The conductor has a length of 20 m and a diameter of 0.7 mm. (i) (ii) (iii) Calculate the current which flows through the copper alloy conductor and the current density in it. What is the electrical conductivity of the material? After a while, the temperature in the copper alloy conductor rises and its resistance becomes 2.4 №. If the temperature coefficient of resistance of the copper alloy is 0.004/°C at 20 °C, calculate the temperature to which the conductor has risen.

(II) A rectangular solid made of carbon has sides of lengths 1.0 cm, 2.0 cm, and 4.0 cm, lying along the x, y, and z axes, respectively (Fig. 18–35). Determine the resistance for current that passes through the solid in (a) the x direc- tion, (b) the y direction, and (c) the z direction. Assume the resistivity is p = 3.0 × 10-$ :m. 2.0 cm FIGURE 18–35 1.0 cm Problem 19. 4.0 cm

1. (a) A certain conductor has a resistance of 10 ohms. It is placed between the poles of a cell whose potential is 5 volts. What current will pass through the conductor if the voltage remains constant at the value given? (b) How many coulombs of electricity will pass through the conductor if this current is maintained for 20 minutes? c) what will be the energy expended during this time interval?

In a certain region of space, the current density is ] = C(x³î + y³ĵ + z³k), being the value of the constant "C" equal to 10-3, the coordinates x, y and z are in meters. I) II) III) Find the units of the constant C. How fast does the charge density "p" (in C/m³.s) change at the point P with coordinates equal to (2, -1, 4) m? Find the rate of change of the electric charge contained in a sphere of radius R=20 cm with center at the origin 0, for a given instant of time.

(I) A service station charges a battery using a current of6.7 A for 5.0 h. How much charge passes through the battery?

Your desk lamp draws a current of 0.20 A for 500 s. How much charge fows through the lamp in this time? How many electrons fow through the lamp in this time? [Answer: (a) ∆Q = 100 C,(b) N = 6.3 × 1020 electrons]

- I A 230-km-long high-voltage transmission line 2.00 cm in diameter carries a steady current of 1,070 A. If the conductor is copper with a free charge density of 8.50 x 1028 electrons per cubic meter, how many years does it take one electron to travel the full length of the cable? (Use 3.156 x 107 for the number of seconds in a year.) yr Need Help? Read It Master It R 20

(II) An electric device draws 5.60 A at 240 V. (a) If thevoltage drops by 15%, what will be the current, assumingnothing else changes? (b) If the resistance of the device werereduced by 15%, what current would be drawn at 240 V?