1. a Legend has it that Isaac Newton was sitting under a tree when an apple fell on his head. It made him think: 'Why do apples always fall straight down, and not to the side?' He later theorised that this happens because there is a force acting on the apple and that this force causes the apple to move towards the Earth.
But let us see if we can explain why the apple falls *without* referring to force.
i When the apple is on the tree, other than its chemical energy, what store of energy does it possess?
ii When the apple falls from the tree what happens to its energy?
iii Do apples ever rise from the ground and move upwards to the tree? Why?
iv So, without reference to force, why do apples fall from a tree towards the ground?
2. b Now let us use the conclusion from part a to see if we can explain why the charged particles in a current are moving. Suppose a wire in which there is a current flowing is lying flat on a table. The current is made up of free electrons drifting along inside the wire.
i What energy transfer is taking place as the free electrons drift along the wire?
ii What is it that makes the free electrons move along the wire? Is your answer essentially the same as it had been for part a iv?
3. c The amount of gravitational potential energy possessed by a mass of 1 kg above the ground is called its ‘gravitational potential’, Vg , and so we can write Vg=massEP .
Similarly, the amount of electrical potential energy possessed by 1 C of charge is called its ‘electrical potential’,
VE=chargeelectrical potential energy.i In the case of the apple, is there a *difference* between the gravitational potential at the tree level and the gravitational potential at the ground level?
ii So does the apple move from the tree to the ground because there is a gravitational *potential difference*?
iii And, in the case of the free electrons in the wire, do the electrons move because there is an electrical potential difference?
iv So, in terms of energy, suggest how *potential difference* might be defined.
v What is the SI unit for electrical potential difference?
vi How do we usually create an electrical potential difference?
a. a Legend has it that Isaac Newton was sitting under a tree when an apple fell on his head. It made him think: 'Why do apples always fall straight down, and not to the side?' He later theorised that this happens because there is a force acting on the apple and that this force causes the apple to move towards the Earth.
But let us see if we can explain why the apple falls *without* referring to force.
i When the apple is on the tree, other than its chemical energy, what store of energy does it possess?
ii When the apple falls from the tree what happens to its energy?
iii Do apples ever rise from the ground and move upwards to the tree? Why?
iv So, without reference to force, why do apples fall from a tree towards the ground?
c. c The amount of gravitational potential energy possessed by a mass of 1 kg above the ground is called its ‘gravitational potential’, Vg , and so we can write Vg=massEP .
Similarly, the amount of electrical potential energy possessed by 1 C of charge is called its ‘electrical potential’,
VE=chargeelectrical potential energy.i In the case of the apple, is there a *difference* between the gravitational potential at the tree level and the gravitational potential at the ground level?
ii So does the apple move from the tree to the ground because there is a gravitational *potential difference*?
iii And, in the case of the free electrons in the wire, do the electrons move because there is an electrical potential difference?
iv So, in terms of energy, suggest how *potential difference* might be defined.
v What is the SI unit for electrical potential difference?
vi How do we usually create an electrical potential difference?
(1) a Legend has it that Isaac Newton was sitting under a tree when an apple fell on his head. It made him think: 'Why do apples always fall straight down, and not to the side?' He later theorised that this happens because there is a force acting on the apple and that this force causes the apple to move towards the Earth.
But let us see if we can explain why the apple falls *without* referring to force.
i When the apple is on the tree, other than its chemical energy, what store of energy does it possess?
ii When the apple falls from the tree what happens to its energy?
iii Do apples ever rise from the ground and move upwards to the tree? Why?
iv So, without reference to force, why do apples fall from a tree towards the ground?
(2) b Now let us use the conclusion from part a to see if we can explain why the charged particles in a current are moving. Suppose a wire in which there is a current flowing is lying flat on a table. The current is made up of free electrons drifting along inside the wire.
i What energy transfer is taking place as the free electrons drift along the wire?
ii What is it that makes the free electrons move along the wire? Is your answer essentially the same as it had been for part a iv?
(3) c The amount of gravitational potential energy possessed by a mass of 1 kg above the ground is called its ‘gravitational potential’, Vg , and so we can write Vg=massEP .
Similarly, the amount of electrical potential energy possessed by 1 C of charge is called its ‘electrical potential’,
VE=chargeelectrical potential energy.i In the case of the apple, is there a *difference* between the gravitational potential at the tree level and the gravitational potential at the ground level?
ii So does the apple move from the tree to the ground because there is a gravitational *potential difference*?
iii And, in the case of the free electrons in the wire, do the electrons move because there is an electrical potential difference?
iv So, in terms of energy, suggest how *potential difference* might be defined.
v What is the SI unit for electrical potential difference?
vi How do we usually create an electrical potential difference?