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## Class 10 Physics (India)

### Course: Class 10 Physics (India) > Unit 3

Lesson 3: Circuits, Ohm's law & resistance# Solved example: Ohms law

Let's solve a couple of numerical on Ohm's law. Created by Mahesh Shenoy.

## Want to join the conversation?

- *Is there a difference between electric potential and electric potential energy?*(4 votes)
- The basic difference between electric potential and electric potential energy is that Electric potential at a point in an electric field is the amount of work done to bring the unit positive charge from infinity to that point, while electric potential energy is the energy that is needed to move a charge against the electric field.

The gravitational potential at a point in the gravitational field is the gravitational potential energy of a unit mass placed at that point. In this way, the electric potential at any point in the electric field is the electric potential energy of a unit positive charge at that point.

If W is the work done in moving a unit positive charge q from infinity to a certain point in the field, the electric potential V at this point is given by:

V = W/q

It implies that electric potential is measured relative to some reference point and like potential energy we can measure only the change in potential between two points.

Electric potential is the scalar quantity. Its unit is volt which is equal to joule per coulomb (J/C).(4 votes)

- Will current flow through zero resistance(3 votes)
- There is no existence of zero resistance no matter which conductor you take. Let's assume there is a conductor which offers no resistance. Current would not flow through that conductor according to ohm's law(1 vote)

- what's the difference between potential energy and potential difference?(1 vote)

## Video transcript

when the potential difference across the filament of a bulb is hundred volts the current through it is found to be 2 amperes find the resistance of the filament so we are asked to calculate what the resistance which we'll call as R of the filament is this is what we need to find and what we are given is the potential difference across the filament of the bulb is hundred volts so if you just draw this let's draw what's given to us so imagine here's the filament here's the filament we are given the potential difference across the filament of the bulb is hundred volts so the potential difference across this n this is hundred volts so V is hundred and the current through it is found to be two amperes so there's a current running through it and this current is 2 amps so I is 2 amps so given this we need to find what the resistance of the filament is so we need a connection between voltage current and resistance and this connection is what we call Ohm's law so um slaw tells us that V should be equal to I times R so if we plug in the values over here we can now calculate the value of R so pause the video and see if you can do this yourself now all right so let's plug in we know the voltage is hundred volts so this is hundred volts that's going to be the current which is 2 amps this is 2 amps times the resistance which we don't know so we calculate the resistance let's divide on both sides by 2 amps the two amps cancel over here and from this we get R equals 100 volts divided by 2 amps 100 by 2 is 50 and so we'll get the resistance to be 50 volts per ampere and volts per ampere is what we often call homes so we will say the resistance is 50 ohms so there we have it the resistance of the filament is 50 ohms okay let's try one more a current of 6 amperes flows through the heating element of an iron box if the resistance of the element is 30 ohms find the potential difference across it so great idea to pause the video and first see if you can gather what is asked write down what the data is and try and solve this problem yourself so pause the video and try and do that first and then we'll solve it all right let's do ok let's do it we are asked to find the potential difference across the element so potential difference is what we need to find V and what we are given is the current of 6 amps flows through the heating element so if we draw let's say this is our heating element I'm just going to draw it as a resistor the current through it is 6 amps and we are given the resistance of the element is 30 ohms so this is 30 ohms so I is given to be 6 amps and R is given to be 30 ohms so we need again a connection between VI and our no surprise we are again going to use Ohm's law we already just saw that Ohm's law says V is I times R V equals IR that's Ohm's law and we can now plug in and get the answer so if you haven't done it already again good time to pause the video and see if you can get the answer yourself now all right let's do this so V is going to be I that's six amps times R which is 30 ohms so V is going to be 6 times 3 it's 180 the unit looks like ampere ohms yeah ampere ohms but if you look at ampere ohms is actually what volt is so we already know the unit of potential difference is volt right and the reason it turns out to be volt is because the ohms is actually volts for ampere or if you just discussed in a previous question right and so the ampere ampere cancels and you end up with walls so we don't have to worry too much about the unit's the current will always be in amps the voltage will always be in volts and the resistance will always be in ohms so out of the three things voltage current and resistance when any two of them are given and we need to find the third one we always use Ohm's law