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Ohm's Law

Lecture Slides are screen-captured images of important points in the lecture. Students can download and print out these lecture slide images to do practice problems as well as take notes while watching the lecture.

  • Intro 0:00
  • Question 1 0:12
  • Question 2 0:33
  • Question 3 0:59
  • Question 4 1:32
  • Question 5 1:56
  • Question 6 2:50
  • Question 7 3:19
  • Question 8 3:50

Transcription: Ohm's Law

Hi everyone and welcome back to

In this mini-lesson, we are going to go over page 1 of the APlusPhysics worksheet on Ohm's Law and you can find the link to that worksheet down below the video.0003

Let us take a look at Number 1 -- Which graph best represents the relationship between the electrical power and the current in the resistor that obeys Ohm's Law?0011

Well, power is current times voltage, so as current goes up, we would expect a linear increase in power.0021

So the correct answer there must be Number 3.0029

Number 2 -- A potential drop of 50 volts is measured across a 250 ohm resistor.0034

What is the power developed in the resistor?0039

Well, power is V2/R, so that will be 50 volts2/250 ohms or 10 W.0042

The correct answer is Number 3.0055

Looking at Number 3 -- How much electrical energy is required to move a 4 micro-coulomb charge through a potential difference of 36 volts?0058

Well, the electrical energy or the work is charged times voltage, which will be 4 × 10-6 micro-coulombs × 36 volts is going to work out to be right around 1.44 × 10-4 J -- Answer is Number 3.0067

Number 4 -- A circuit consists of a resistor in a battery.0090

Increasing the voltage of the battery, while keeping the temperature of the circuit constant would result in an increase in...?0095

Well, I = V/R. If the temperature is constant, then (R) should be constant if we increase the voltage, we should get an increase in current only, so the correct answer to 4 is Number 1.0101

Number 5 -- A generator produces 115 volt potential difference in a maximum of 20 A of current.0116

Find the total electrical energy the generator produces operating at maximum capacity for 60 seconds.0124

We are looking for energy and we are given voltage and current.0130

The way I would do this is realizing that power, which is W/t or E/t is also equal to current time's voltage.0135

Therefore the energy (W) is going to be current × voltage × time or 20 A × 115 volts × 60 s, which is going to give us an energy of right around 138,000 J or 138 kJ.0142

Moving on to Number 6 -- An electric circuit contains a variable resistor connected to a source of constant voltage.0169

As the resistance of the variables that resistor has increased, the power dissipated does what?0177

Power equals V2/R and our voltage is constant, so as the resistance is increased the power dissipated must decrease, so for Number 6 our correct answer is Number 1.0183

Number 7 -- An electric circuit contains a variable resistor connected to a source of constant potential difference.0200

Which graph best represents the relationship between current and resistance in that circuit?0206

Current equals V/R by Ohm's Law and now we have a constant potential difference.0212

What happens is resistance goes up and current must go down. Our answer there must be Number 1.0219

One more -- Number 8 -- In a simple electric circuit a 24 ohm resistor is connected across a 6 volt battery.0229

What is the current?0236

Current equals V/R or 6 volts/24 ohms is going to be 0.25 A, so the correct answer is Number 2.0239

All right. That completes page 1 of the worksheet on Ohm's Law.0252

If this went well -- Terrific -- time to move on, but if you struggled with this a little bit, it is probably a good idea to go back and review the video, the lesson on Ohm's Law.0256

Thanks so much for your time everyone and make it a great day!0265