Electric Current Problems: Calculating Current, Charge, and Resistance, Exams of Circuit Theory

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ELECTRIC CURRENT

Mr. Charge’s Journey

PROBLEM

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?

PROBLEM

1 x 10 20 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)

B)

t 3 s

Q 16 C

1 e

1 6 10 C

Q 1 10 e e 1 10 e 19 20 20 

 .

A s C t Q I 5. 33 3 16   

t s Q I A 5 8    ?

2.5 10 e

1e

# 40C

Q I t 8 5

t

Q

I

20 19



PROBLEM

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?

PROBLEM

How many electrons pass a point in 10 s if a constant current of 20 A is maintained in a conductor?

t s Q I A 10 20    ?

# 200 6.25 10 1.25 10 e

Q I t 20 10

t

Q

I

18 21

t 1 s

Q

electrons 1 10

I

18

16 A 1 s 16 C t Q I Q 1 10 1 6 10 16 C 18 19 . . (. ).        

PROBLEM

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?

PROBLEM

Find the resistance of a portable lantern that uses a 24 V power supply and draws a current of 0.80 A.

? 24

. 80    R V V I A    30  80 24 I****. V R

? 120

1. 50    R V V I A    240 
2. 5 120 I V R

PROBLEM

An automobile headlight with a resistance of 30 ohms is placed across a 12 V battery. What is the current through the circuit?