Back(III) The filament of an incandescent lightbulb has a resistance of 12 Ω at 20°C and 140 Ω when hot. In this temperature range, what is the percentage change in resistance due to thermal expansion, and what is the percentage change in resistance due solely to the change in ρ? Use Eq. 25–5.
An idealized ammeter is connected to a battery as shown in Fig. E. Find the terminal voltage of the battery.
In household wiring, copper wire mm in diameter is often used. Find the resistance of a -m length of this wire.
A zener diode voltage regulator is shown in Fig. 40–55. Suppose that R = 2.80 kΩ and that the diode breaks down at a reverse voltage of 130 V. (The current increases rapidly at this point, as shown on the far left of Fig. 40–38 at a voltage of -12V on that diagram.) The diode is rated at a maximum current of 120 mA. (a) If Rload = 21.0 kΩ, over what range of supply voltages will the circuit maintain the output voltage at 130 V? (b) If the supply voltage is 275 V, over what range of load resistance will the voltage be regulated?
Two resistors are made of the same material, one twice as long as the other. If the current through the shorter resistor is 5 A, what is the current through the longer resistor if they both have the same potential difference and cross-sectional area?
A hollow metal cylinder has inner radius a, outer radius b, length L, and conductivity σ. The current I is radially outward from the inner surface to the outer surface. Evaluate the electric field strength at the inner and outer surfaces of an iron cylinder if a=1.0 cm, b=2.5 cm, L=10 cm, and I=25 A.
According to Ohm's Law, how many ohms of resistance will allow a current of to flow when a voltage of is applied across a resistor?
The resistance of a very fine aluminum wire with a 10 μm ×10 μm square cross section is 1000 Ω . A 1000 Ω resistor is made by wrapping this wire in a spiral around a 3.0-mm-diameter glass core. How many turns of wire are needed?
Which of the following is one function of a resistor in a circuit?
The cross section of a portion of wire increases uniformly as shown in Fig. 25–38 so it has the shape of a truncated cone. The diameter at one end is a and at the other it is b, and the total length along the axis is ℓ. If the material has resistivity ρ, determine the resistance R between the two ends in terms of a, b, ℓ, and ρ. Assume that the current flows uniformly through each section, and that the taper is small, i.e., ( b -a) ≪ ℓ.
Eight identical bulbs are connected in series across a 120-V line. What is the voltage across each bulb?
Electrical engineers sometimes use a wire's conductance, G=σA/L, instead of its resistance. A 1.5 A current flows through the wire of part b. What is the potential difference between the ends of the wire?
According to Ohm's Law, what is the relationship between the current and the voltage across a resistor in a circuit?
Variations in the resistivity of blood can give valuable clues about changes in various properties of the blood. Suppose a medical device inserts microelectrodes into a 1.5-mm-diameter vein at positions 5.0 cm apart. What is the blood resistivity if a 9.0 V potential difference causes a 230 μA current through the blood in the vein?
In a cylindrical resistor, what is the effect on the resistance if the radius of the vessel is halved, assuming the length and material remain constant? (The resistance of a cylinder is given by , where is resistivity, is length, and is radius.)