Video Transcript
The diagram shows a circuit
consisting of a cell and a bulb. The bulb has a resistance of 20
ohms, and the current in the circuit is 1.5 amperes. What is the potential difference
provided by the cell?
Okay, so in this question, we have
a bulb that we’re told has a resistance of 20 ohms. We’ll label this resistance as 𝑅
so that we have 𝑅 is equal to 20 ohms. This bulb is connected to a
cell. And we’re told that there is a
current in the circuit of 1.5 amperes. Labeling this current as 𝐼, we
have that 𝐼 is equal to 1.5 amperes. We are asked to work out the
potential difference provided by the cell. And we’ll label this potential
difference as 𝑉.
We can recall that these three
quantities are linked by an equation known as Ohm’s law. Specifically, Ohm’s law tells us
that potential difference 𝑉 is equal to current 𝐼 multiplied by resistance 𝑅. So now we can go ahead and
substitute these values for 𝐼 and 𝑅 into this Ohm’s law equation. When we do this, we find that 𝑉 is
equal to 1.5 amperes, so that’s our value for 𝐼, multiplied by 20 ohms. That’s our value for 𝑅.
We have a current in units of
amperes and a resistance in units of ohms. So that means that we’re going to
get a potential difference in units of volts. When we evaluate this expression,
we find that 𝑉 is equal to 30 volts. This value of 𝑉 is the potential
difference across the bulb in our circuit, which must be the same as the potential
difference provided by the cell. And so our answer to the question
is that the potential difference provided by the cell is 30 volts.
