Understanding Electric Current Concepts through Practice Problems
Explore electric current concepts through a series of problems involving charge, current, and electron flow in circuits. Practice calculating current, charge flow, and electron quantities in different scenarios to deepen your understanding of electrical principles.
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ELECTRIC CURRENT Mr. Charge s Journey
PROBLEM #1 The amount of charge that passes through the filament of a certain light bulb in 2 seconds is 1.67 C. A) What is the current in the light bulb? B) What is the number of electrons that pass through the filament in one second?
Q . 1 67 A) = = = I A . 0 835 t 2 s s 2 2 In In 1.67 1.67 C C of of charge charge passes passes B) : : s s 1 1 In In 0.835C 0.835C of of charge charge will will pass pass 1e 1e 0.835C 0.835C 19 19 - - 1.6 1.6 18 18 10 10 C C 5.22 5.22 10 10 electrons electrons =
PROBLEM #2 1 x 1020 electrons flow through a conductor in 3 s. A) What is the charge flowing through the conductor? B) What is the current in the circuit?
A) = 20 e 1 10 e # 19 1 6 . 10 C = 20 Q 1 10 e e 1 = Q 16 C = t s 3 Q C 16 B) = = = I A . 5 33 t s 3
PROBLEM #3 How many electrons pass a point in 5 s if a constant current of 8 A is maintained in a conductor?
= = I A ? 8 = = Q = = t s 5 Q Q I I = t t Q Q I I t t 8 8 5 5 = = 1e 1e 20 20 # # 40C 40C 2.5 2.5 10 10 e e = = 19 19 1.6 1.6 10 10
PROBLEM #4 The amount of charge that passes through the filament of a certain light bulb in 2 seconds is 12C. A) What is the current in the light bulb? B) What is the number of electrons that pass through the filament in one second?
Q 12= = = I A 6 A) t 2 B) Current means A 6 of 6 C of charge will through pass ( second. 1 in = 18 19 6 6.25 10 3 75 . 10 electrons )
PROBLEM #5 How many electrons pass a point in 10 s if a constant current of 20 A is maintained in a conductor?
= = I A 20 ? = = Q = = t s 10 Q Q I I = t t Q Q I I t t 20 20 10 10 = = 18 18 21 21 # # 200 200 6.25 6.25 ( 10 10 1.25 1.25 10 10 e e = = )
PROBLEM #6 How many amperes of current flow in a wire through which 1018 electrons pass per second?
= I # ? = 18 electrons = ? 1 10 Q s 1 = t = = 18 19 Q 1 10 1 6 . 10 16 . C ( ) Q 16 . C = = = I 16 . A t s 1
PROBLEM #7 The headlights of a typical car are powered by a 12 V battery. What is the resistance of the headlights if they draw 3 A of current when turned on?
= = I A 12 3 = = V V = = R ? V 12 = = = = = = 4 R I 3
PROBLEM #8 Find the resistance of a portable lantern that uses a 24 V power supply and draws a current of 0.80 A.
= I A 80 . = V V 24 = R ? V 24 = = = = = = R 30 I 80 .
PROBLEM #9 The current in a resistor of is 0.50 A when connected across a voltage of 120V. What is its resistance?
= I A . 0 = 50 V V 120 = R ? V 120 = = = R 240 I 5 . 0
PROBLEM #10 An automobile headlight with a resistance of 30 ohms is placed across a 12 V battery. What is the current through the circuit?
= I ? = V V 12 = R 30 V 12= = = I A 4 . 0 R 30
PROBLEM #11 A motor with an operating resistance of 32 ohms is connected to a voltage source. The current in the circuit is 3.8 A. What is the voltage of the voltage source?
= I A 8 . 3 = V ? = R 32 = ( 8 . 3 = = V IR V 32 ) 121 6 .
PROBLEM #12 A transistor radio uses 0.0002 A of current, when a 3 V battery operates it. What is the resistance of the radio circuit?
= I A 0002 . 0 = V V 3 = R ? V 3 = = = R 15000 I 0002 . 0
PROBLEM #13 What is the resistance of an electric frying pan that draws 12 amperes of current when connected to a 120 V circuit?
= I A 12 = V V 120 = R ? V 120 = = = R 10 I 12
PROBLEM #14 How much current is drawn by a lamp that has a resistance of 100 ohms when a voltage of 50 volts is impressed across it?
= I ? = V V 50 = R 100 V 50= = = I A 5 . 0 R 100
PROBLEM #15 The plate on a certain steam iron states that the iron carries a current of 6.4 A when connected to a 120 V source. What is the resistance of the steam iron?
= I A 4 . 6 = V V 120 = R ? V 120 = = = R 18 75 . I 4 . 6
PROBLEM #16 The resistance of the hot plate is 48 ohms. How much current does the plate carry when connected to a 120 V source?
= I ? = V V 120 = R 48 V 120= = = I A 5 . 2 R 48
EXAMPLE 1 A heater has a resistance of 10 . It operates on 120 V. A) What is the current through the resistance? B) What thermal energy is supplied to the heater in 10 s?
V 120 = = = I 12 A R 10 = E Pt = VIt = 120 12 ( 10 )( ) = 14400 J
EXAMPLE 2 A current of 6 A flows through a resistance of 300 for one hour. What is the power loss? How much heat is generated in joules?
= = = V IR 6 300 1800 V ( ) = P VI = 1800 6 ( ) = 10800 W = E P t = 10800 W 3600 s ( ) = 7 3 8 . 10 J
PROBLEM #17 A 15 ohm electric heater operates on a 120 V outlet. A) What is the current through the heater? B) How much energy does the heater liberate in 30 seconds? C) How much thermal energy does the heater liberate in this time?
V 120 = = = I 8 A R 15 = E Pt = VIt = 120 8 30 ( )( ) = 28800 J
PROBLEM #18 A 30-ohm resistor is connected across a 60 V battery. A) What is the current in the circuit? B) How much energy does the resistor use in 5 minutes?
V 60 = = = I 2 A R 30 = E Pt = VIt = 60 2 5 60 ( )( )( ) = 36000 J
PROBLEM #19 A soldering iron draws 0.75 A at 120 V. How much energy does the resistor use in 15 minutes?
= E Pt = VIt = 120 75 15 60 (. )( )( ) = 81000 J
PROBLEM #20 An electric lamp has an 80 ohm filament connected to a 110 V direct current line. What is the current through the filament? What is the power loss in watts?
V 110 = = = I 1 375 . A R 80 = P VI = 110 1 375 . ( ) = 151 25 . W
PROBLEM #21 How much does it cost to burn 100 W light bulb for 24 hours if the electrical energy costs $0.08 per kilowatt-hour?
= = P 100 W 0 kW 1 . = t 24 h = = = E Pt 0 kW 1 . 24 h 2 kWh 4 . ( ) 08 $. = = Cost 2 kWh 4 . 0 192 . ( ) $ kWh
PROBLEM #22 A modern color TV set draws 2 A when operated on 120 V. A) How much power does the set use? B) If the set is operated for an average of 7 hours/day, what energy in kWh does it consume per month (30 days) C) At $0.11 per kWh, what is the cost of operating the set per month?
A) = P VI = = = 120 V 2 A 240 W 240 . kW ( ) = E Pt B) = = 240 . kW 7 30 $. h 50 kWh 4 . ( )( ) 11 = = Cost 50 kWh 4 . 5 544 . ( ) $ C) kWh
PROBLEM #23 An electric space heater draws 20 A from a 120V source. It is operated on the average of 5 hours each day. A) How much power does the heater use? B) How much energy in kWh does it consume in 30 days? C) At $.11 per kWh, what does it cost to operate it for 30 days?
