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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.


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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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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

how vapour pressure of a liquid lost through convection
Yomzi Reply
Roofs are sometimes pushed off vertically during a tropical cyclone, and buildings sometimes explode outward when hit by a tornado. Use Bernoulli’s principle to explain these phenomena.
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what's the basic si unit of acceleration
Explain why the change in velocity is different in the two frames, whereas the change in kinetic energy is the same in both.
Fabian Reply
Insulators (nonmetals) have a higher BE than metals, and it is more difficult for photons to eject electrons from insulators. Discuss how this relates to the free charges in metals that make them good conductors.
Muhammad Reply
Is the photoelectric effect a direct consequence of the wave character of EM radiation or of the particle character of EM radiation? Explain briefly.
Determine the total force and the absolute pressure on the bottom of a swimming pool 28.0m by 8.5m whose uniform depth is 1 .8m.
Henny Reply
how solve this problem?
P(pressure)=density ×depth×acceleration due to gravity Force =P×Area(28.0x8.5)
for the answer to complete, the units need specified why
muqaddas Reply
That's just how the AP grades. Otherwise, you could be talking about m/s when the answer requires m/s^2. They need to know what you are referring to.
Suppose a speck of dust in an electrostatic precipitator has 1.0000×1012 protons in it and has a net charge of –5.00 nC (a very large charge for a small speck). How many electrons does it have?
Alexia Reply
how would I work this problem
how can you have not an integer number of protons? If, on the other hand it supposed to be 1e12, then 1.6e-19C/proton • 1e12 protons=1.6e-7 C is the charge of the protons in the speck, so the difference between this and 5e-9C is made up by electrons
what is angular velocity
Obaapa Reply
angular velocity can be defined as the rate of change in radian over seconds.
Why does earth exert only a tiny downward pull?
Mya Reply
Why is light bright?
Abraham Reply
what is radioactive element
Attah Reply
an 8.0 capacitor is connected by to the terminals of 60Hz whoes rms voltage is 150v. a.find the capacity reactance and rms to the circuit
Aisha Reply
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Valdes Reply
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Nwafor Reply
is the study of matter in relation to energy
physics can be defined as the natural science that deals with the study of motion through space,time along with its related concepts which are energy and force
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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