This question is in two parts. Part 1 is about a lightning discharge. Part 2 is about fuel for heating.
## Part 1 Lightning discharge
6a. Define *electric field strength*.
6b. A thundercloud can be modelled as a negatively charged plate that is parallel to the ground.
The magnitude of the charge on the plate increases due to processes in the atmosphere. Eventually a current discharges from the thundercloud to the ground.
On the diagram, draw the electric field pattern between the thundercloud base and the ground.
The magnitude of the electric field strength E between two infinite charged parallel plates is given by the expression
E=ϵ0σ
where σ is the charge per unit area on one of the plates.
A thundercloud carries a charge of magnitude 35 C spread over its base. The area of the base is 1.2×107 m2.
6c. (i) Determine the magnitude of the electric field between the base of the thundercloud and the ground.
(ii) State two assumptions made in (c)(i).
(iii) When the thundercloud discharges, the average discharge current is 1.8 kA. Estimate the discharge time.
(iv) The potential difference between the thundercloud and the ground before discharge is 2.5×108 V. Determine the energy released in the discharge.
## Part 2 Fuel for heating
6d. Define the *energy density* of a fuel.
A room heater burns liquid fuel and the following data are available.
Density of liquid fuel =8.0×102 kg m−3
Energy produced by 1 m3 of liquid fuel =2.7×1010 J
Rate at which fuel is consumed =0.13 g s−1
Latent heat of vaporization of the fuel =290 kJ kg−1
6e. (i) Use the data to calculate the power output of the room heater, ignoring the power required to convert the liquid fuel into a gas.
(ii) Show why, in your calculation in (b)(i), the power required to convert the liquid fuel into a gas at its boiling point can be ignored.
6f. State, in terms of molecular structure and their motion, two differences between a liquid and a gas.