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The figure shows a simple electric circuit. A battery is connected to a resistor with resistance R, and a voltmeter is connected across the resistor. The direction of current is shown to emerge from the positive terminal of the battery of voltage V, pass through the resistor, and enter the negative terminal of the battery, in a clockwise direction. The voltage V in the circuit equals I R, which equals 18 volts.
The voltage drop across a resistor in a simple circuit equals the voltage output of the battery.

Making connections: conservation of energy

In a simple electrical circuit, the sole resistor converts energy supplied by the source into another form. Conservation of energy is evidenced here by the fact that all of the energy supplied by the source is converted to another form by the resistor alone. We will find that conservation of energy has other important applications in circuits and is a powerful tool in circuit analysis.

Phet explorations: ohm's law

See how the equation form of Ohm's law relates to a simple circuit. Adjust the voltage and resistance, and see the current change according to Ohm's law. The sizes of the symbols in the equation change to match the circuit diagram.

Ohm's Law

Test prep for ap courses

If the voltage across a fixed resistance is doubled, what happens to the current?

  1. It doubles.
  2. It halves.
  3. It stays the same.
  4. The current cannot be determined.

(a)

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The table below gives the voltages and currents recorded across a resistor.

Voltage (V) 2.50 5.00 7.50 10.00 12.50
Current (A) 0.69 1.38 2.09 2.76 3.49
  1. Plot the graph and comment on the shape.
  2. Calculate the value of the resistor.
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What is the resistance of a bulb if the current in it is 1.25 A when a 4 V voltage supply is connected to it? If the voltage supply is increased to 7 V, what will be the current in the bulb?

3.2 Ω, 2.19 A

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Section summary

  • A simple circuit is one in which there is a single voltage source and a single resistance.
  • One statement of Ohm's law gives the relationship between current I , voltage V , and resistance R in a simple circuit to be I = V R . size 12{I = { {V} over {R} } } {}
  • Resistance has units of ohms ( Ω ), related to volts and amperes by 1 Ω = 1 V/A size 12{1 %OMEGA =" 1 V/A"} {} .
  • There is a voltage or IR size 12{ ital "IR"} {} drop across a resistor, caused by the current flowing through it, given by V = IR size 12{V = ital "IR" } {} .

Conceptual questions

The IR size 12{ ital "IR"} {} drop across a resistor means that there is a change in potential or voltage across the resistor. Is there any change in current as it passes through a resistor? Explain.

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How is the IR size 12{ ital "IR"} {} drop in a resistor similar to the pressure drop in a fluid flowing through a pipe?

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Problems&Exercises

What current flows through the bulb of a 3.00-V flashlight when its hot resistance is 3 . 60 Ω size 12{3 "." "60" %OMEGA } {} ?

0.833 A

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Calculate the effective resistance of a pocket calculator that has a 1.35-V battery and through which 0.200 mA flows.

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What is the effective resistance of a car's starter motor when 150 A flows through it as the car battery applies 11.0 V to the motor?

7 . 33 × 10 2 Ω size 12{7 "." "33"´"10" rSup { size 8{-2} } %OMEGA } {}

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How many volts are supplied to operate an indicator light on a DVD player that has a resistance of 1 40 Ω size 12{1"40 " %OMEGA } {} , given that 25.0 mA passes through it?

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(a) Find the voltage drop in an extension cord having a 0 . 0600- Ω size 12{0 "." "0600-" %OMEGA } {} resistance and through which 5.00 A is flowing. (b) A cheaper cord utilizes thinner wire and has a resistance of 0 . 300 Ω size 12{0 "." "300" %OMEGA } {} . What is the voltage drop in it when 5.00 A flows? (c) Why is the voltage to whatever appliance is being used reduced by this amount? What is the effect on the appliance?

(a) 0.300 V

(b) 1.50 V

(c) The voltage supplied to whatever appliance is being used is reduced because the total voltage drop from the wall to the final output of the appliance is fixed. Thus, if the voltage drop across the extension cord is large, the voltage drop across the appliance is significantly decreased, so the power output by the appliance can be significantly decreased, reducing the ability of the appliance to work properly.

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A power transmission line is hung from metal towers with glass insulators having a resistance of 1 . 00 × 10 9 Ω . size 12{1 "." "00"´"10" rSup { size 8{9} } %OMEGA } {} What current flows through the insulator if the voltage is 200 kV? (Some high-voltage lines are DC.)

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Questions & Answers

Propose a force standard different from the example of a stretched spring discussed in the text. Your standard must be capable of producing the same force repeatedly.
Giovani Reply
What is meant by dielectric charge?
It's Reply
what happens to the size of charge if the dielectric is changed?
Brhanu Reply
omega= omega not +alpha t derivation
Provakar Reply
u have to derivate it respected to time ...and as w is the angular velocity uu will relace it with "thita × time""
Abrar
do to be peaceful with any body
Brhanu Reply
the angle subtended at the center of sphere of radius r in steradian is equal to 4 pi how?
Saeed Reply
if for diatonic gas Cv =5R/2 then gamma is equal to 7/5 how?
Saeed
define variable velocity
Ali Reply
displacement in easy way.
Mubashir Reply
binding energy per nucleon
Poonam Reply
why God created humanity
Manuel Reply
Because HE needs someone to dominate the earth (Gen. 1:26)
Olorunfemi
why god made humenity
Ali
Is the object in a conductor or an insulator? Justify your answer. whats the answer to this question? pls need help figure is given above
Jun Reply
ok we can say body is electrically neutral ...conductor this quality is given to most metalls who have free electron in orbital d ...but human doesn't have ...so we re made from insulator or dielectric material ... furthermore, the menirals in our body like k, Fe , cu , zn
Abrar
when we face electric shock these elements work as a conductor that's why we got this shock
Abrar
how do i calculate the pressure on the base of a deposit if the deposit is moving with a linear aceleration
ximena Reply
why electromagnetic induction is not used in room heater ?
Gopi Reply
room?
Abrar
What is position?
Amoah Reply
What is law of gravition
sushil Reply
Practice Key Terms 5

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Source:  OpenStax, College physics for ap® courses. OpenStax CNX. Nov 04, 2016 Download for free at https://legacy.cnx.org/content/col11844/1.14
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