Electric Fields (Edexcel A Level Physics): Exam Questions

Our understanding of the atom has developed over time, from early models in which atoms were considered to be hard incompressible spheres, through to the nuclear model of the atom and the ladder model in which electrons exist in a discrete number of allowed energy states.

The model of atoms as hard incompressible spheres, moving rapidly and randomly, can be used to explain why gases exert a pressure.

Explain, using ideas of momentum, why the pressure exerted by a gas increases as the temperature of the gas increases.

The nuclear model of the atom was established following a series of experiments in which alpha particles were directed at thin gold foil.

i) An alpha particle approaching a gold nucleus, ${}_{79}{}^{197}\mathrm{Au}$, head-on will be brought to rest and returned along its original path.

Calculate the minimum distance between the alpha particle and the nucleus for alpha particles of energy of 5.5 MeV.

Minimum distance = ................................(4)

ii) It is observed that electrons, with energy of 5.5 keV, are diffracted as they pass through the thin gold foil.

Explain a conclusion about the electrons that can be made from this observation.

(3)

In the energy ladder model of the atom, electrons exist in a discrete number of allowed energy states. The collision of electrons with gold atoms may lead to the production of high frequency electromagnetic radiation.

Explain how high frequency electromagnetic radiation may be produced when electrons collide with atoms in a metal.

Some flowers are negatively charged and surrounded by an electric field. This helps to attract bees.

State what is meant by an electric field.  

The diagram shows lines of equipotential surrounding a flower. 

i) Determine the electric field strength at X. 

Electric field strength at X = .........................................(3)

ii) Draw the electric field line between point A and point B on the diagram.

(2)

iii) An equation for electric potential V is

$V=\frac{Q}{4\pi {\epsilon }_{0}r}$

This applies to a radial field.

Deduce whether the electric field in the region directly above the flower is radial. You should take values from the diagram. A graphical method is not required. 

(3)

A bee has short hairs which are thought to carry charge.

State how the bee might use this to detect the electric field of a flower.  

When the bee is collecting nectar from the plant, the electric field strength decreases.

It is thought that this warns other bees that the nectar supply is low.

State the effect of a decreased electric field strength on the equipotential lines.