This question is in two parts. Part 1 is about energy resources. Part 2 is about electric fields.
## Part 1 Energy resources
3a. The Sun is a renewable energy source whereas a fossil fuel is a non-renewable energy source. Outline the difference between renewable and non-renewable energy sources.
3b. With reference to the energy transformations and the operation of the devices, distinguish between a photovoltaic cell and a solar heating panel.
A photovoltaic panel is made up of a collection (array) of photovoltaic cells. The panel has a total area of 1.3 m2 and is mounted on the roof of a house. The maximum intensity of solar radiation at the location of the panel is 750 W m−2. The panel produces a power output of 210 W when the solar radiation is at its maximum intensity.
3c. Determine the efficiency of the photovoltaic panel.
3d. State two reasons why the intensity of solar radiation at the location of the panel is not constant.
The owner of the house chooses between photovoltaic panels and solar heating panels to provide 4.2 kW of power to heat water. The solar heating panels have an efficiency of 70%. The maximum intensity of solar radiation at the location remains at 750 W m−2.
3e. Calculate the minimum area of solar heating panel required to provide this power.
3f. Comment on whether it is better to use a solar heating panel rather than an array of photovoltaic panels for the house. Do not consider the installation cost of the panels in your answer.
## Part 2 Electric fields
An isolated metal sphere is placed in a vacuum. The sphere has a negative charge of magnitude 12 nC.
3g. Using the diagram, draw the electric field pattern due to the charged sphere.
Outside the sphere, the electric field strength is equivalent to that of a point negative charge of magnitude 12 nC placed at the centre of the sphere. The radius r of the sphere is 25 mm.
3h. Show that the magnitude of the electric field strength at the surface of the sphere is about 2×105 N C−1.
3i. On the axes, draw a graph to show the variation of the electric field strength E with distance d from the centre of the sphere.
An electron is initially at rest on the surface of the sphere.
3j. Calculate the initial acceleration of the electron.
3k. Discuss the subsequent motion of the electron.