Potential Difference Define potential difference. Define the volt. Solve problems about potential difference. Explain the concept of zero potential.

Potential Difference When an electric field would cause a charge to accelerate between two points, we say there is a potential difference between them. The potential difference, V (aka voltage) between two points is the work required per unit charge to transfer a charge from one point to the other. Formula: 𝑉= 𝑊 𝑄 The unit of potential difference is the volt (V). 1 volt = 1 joule per coulomb

Potential Difference e.g. the potential difference between two points is 12 V. Find the work done in transferring a charge of 8 C between the two points.

Potential Difference e.g. An electron of charge 1.6× 10 −19 C loses 4× 10 −16 J of energy as it moves from one point to another. What is the potential difference between the two points?

Potential Difference e.g. The potential difference between two points is 2000 V. An electron (of charge 1.6× 10 −19 C and mass 9 × 10 −31 kg) is released from rest at one of the points and moves towards the other under the action of the field. Find its speed when it arrives at the second point.

Zero Potential So far we have only discussed potential difference. Scientists sometimes use Earth as a reference for other potentials. Since the Earth is so big and massive, any charge we could realistically add to it will have almost no effect on its total charge, so it is pretty much constant. We say the Earth is at zero potential and call the potential difference between a point and the Earth the potential of that point.

Zero Potential Some books also discuss “zero potential difference”. Due to Coulomb’s Law, we know that the force between charges falls off rapidly with distance. Since force∝𝑤𝑜𝑟𝑘 and 𝑤𝑜𝑟𝑘∝𝑝𝑜𝑡𝑒𝑛𝑡𝑖𝑎𝑙 𝑑𝑖𝑓𝑓𝑒𝑟𝑒𝑛𝑐𝑒, we can say that far away charges have zero potential difference between them. This is fortunate since we can isolate our experiments quite easily by neutralising the surrounding area.