Iona Prep Physics Problems from the textbook
#1 The current through a lightbulb connected across the terminals of a 125 V outlet is 0.50 A. At what rate does the bulb convert electric energy to light?
#2 A car battery causes a current of 2.0 A through a lamp and produces 12 V across it. What is the power used by the lamp?
#3 What is the current through a 75 W light bulb that is connected to a 125 V outlet?
#4 The current through the starter motor of a car is 210 A. If the battery maintains 12 V across the motor, how much electric energy is delivered to the starter in 10.0 s?
#5 A flashlight bulb is rated at 0.90 W. If the lightbulb drops 3.0 V, how much current goes through it?
(Extra) An electric toaster consumes 1875 W in operation. Assuming it is plugged into a 125 V source, what current flows in the circuit?
AA-22-3 A heating element of an electric furnace consumes 5.0 x10^3 W when connected across a 240 V source. What current flows through the element?
AA-22-4 The cold filament resistance of a lightbulb is 20.0 ohms. The bulb consumes 75 W when it is operating from 120V. By what factor does the start-up current in the bulb exceed the operating current?
#9 A lamp draws a current of 0.50 A when it is connected to a 120 V source. (a) What is the resistance of the lamp? (B) What is the power consumption of the lamp?
# 10. A 75 W lamp is connected to 125 V. (A) What is the resistance of the lamp? (B) What is the power consumpton of the lamp?
#20 A circuit has 12 ohms of resistance and is connected to a 12 V battery. Determine the change in power if the resistance decreases to 9.0 ohms.
#21 A circuit converts 2.2x10^3 J of energy when it is operated for 3.0 minutes. Determine the amount of energy it will convert when it is operated for 1 hour.
#23 A 15 ohm electric heater operates on a 120 volt outlet. (A) What is the current through the heater? (B) How much energy is used by the heater in 30 seconds? (C) How much heat energy is liberated in this time?
#26 The resistance of an electric stove element at operating temperature is 11 ohms. (A) If 220 V are applied across it, what is the current through the stove element? (B) How much energy does the element convert to thermal energy in 30 seconds? (C) The element is used to heat a kettle containing 1.20 kg of water. Assume that 65 percent of the heat is absorbed by the water. What is the water's increase in temperature during the 30 seconds?
#27 A 120 V water heater takes 2.2 hours to heat a given volume of water to a certain temperature. How long would a 240 V unit operating with the same current take to accomplish the task?
#28 An electric space heater draws 13.0 A from a 120 V source. It is operated on the average for 5.0 hours each day. (A) How much power does the heater draw? (B) How much energy in kWh (kilowatt-hours) does it consume in 30 days? (C) If electricity costs $0.12 per kWh, how much does it cost to operate the heater for 30 days?
#60 Two wires can be placed across the terminals of a 6.0 volt battery. One has a high resistance, and the other has a low resistance. Which wire will produce thermal energy at a faster rate? Why?
#66 A current of 1.2 A is measured through a light bulb when it is connectetd across a 120 volt source. What power is dissipated by the bulb?
#86 A heater with an effective resistance of 4.8 ohms is connected to 240.0 volts. If it operates approximately 25% of the time, and electricity costs $0.10 per kWh, what will be the electrical bill for 30 days?
#64 A 22 ohm lamp and a 4.5 ohm lamp are connected in series and placed across a potential difference of 45 volts. (a) what is the equivalent resistance of the circuit? (b)What is the current in the circuit? (c) What is the voltage drop across each lamp? (d) What is the power dissipated in each lamp?
#65 A 35 ohm resistor and a 15 ohm resistor are connected in series and the combination is connected to a 10 volt battery. What will be the current in the circuit? (b) What would be the voltage across the 35 ohm resistor? (c) What would be the voltage across the 15 ohm resistor? (d) How much energy is supplied by the battery each minute?
#71 A string of 18 identical Christmas lights is connected in series to a 120 volt source. The string dissipates 64 Watts. (a)What is the resistance of the light string? (b)What is the resistance of a single light? (c) What power is dissipated by each light?
#72 One of the lights in problem 71 burns out. The light shorts out the bulb filament when it burns out. This drops the resistance of that bulb to zero. (a) What is the equivalent resistance of the light string now? (b)Find the power dissipated by the string. (c) Did the power increase or decrease when the bulb burned out?
#73 A 16 ohm and a 20.0 ohm resistor are connected in parallel. A difference in potential of 40.0 volts is applied to the combination. (a) Compute the equivalent resistance of the parallel circuit. (b) What is the total current in the circuit? (c) What is the current in the 16 ohm resistor?
#75 Pete is designing a voltage divider using a 12 volt battery and an 82 ohm resistor as Rb. What resistor should be used as Ra if the output voltage across Rb is to be 4.0 volts?
#77 Assume each resistor is 30 ohms and find the total resistance of the circuit.
81. Find (A) The total resistance (B) The current through the 25 ohm resistor (C) Which resistor will be the hottest.
86. The diagram below shows a typical house circuit.
The wires to the kitchen lamp each have a resistance of 0.25 ohms. Determine the equivalent resistance of the circuit consisting of just the lamp and the lead lines to and from the lamp. Also find the current in the lamp and the power dissipated in the lamp.
93. Determine the maximun voltage that can be applied across the three series resistors below if each is rated at 5.0 watts.
95. Determine the maximum safe voltage thaqt can be applied across three parallel resistors of 92 ohms, 150 ohms, 220 ohms, if all three are rated at 5 W.
99. A battery consists of an ideal source of potential difference in series with a small resistance. The electric energy of the battery is produced by chemical reactions that occur in the battery. However, those reactions also result in a small resistance that, unfortunately, cannot be completely eliminated. A flashlight contains two betteries in series. Each has a potential difference of 1.50 volts and an internal resistance of 0.200 ohms. The bulb has a resistance of 22.0 ohms. (A) What is the current through the bulb? (B) How much greater would the power be if there were no internal resistance?
100. An ohmmeter is made by connecting a 6.0 volt battery in series with an adjustable resistor and an ideal ammeter. The ammeter defelcts full-scale with a current of 1.0 mA. The two leads are touched together and the ressitance is adjusted so that 1.0 mA flows. (A) What is the resistance of the adjustable resistor? (B) What resistance would produce a current of half-scale, 0.5 mA? (C)What resistance would produce a current of quarter scale 0.25 mA? (D) Three-quarters-scale, 0.75 mA? (E) Is the ohmmeter scale linear?