WAEC Air Conditioning(Ac)/Rerigeration May/June 2019 Questions and Answers

WAEC Air Conditioning(Ac)/Rerigeration May/June 2019 Questions and Answers

Question 1

1a.  Define the following terms:

1. work;
2. power;
3. energy.

b.    Draw the pressure enthalpy diagram and show the following processes:

1. compression;
2. condensation;
3. vapourization;
4. expansion.

Observation

Question 1b required the candidates to draw the Pressure-Enthalpy diagram showing the various stages in refrigeration. The expected drawing is:

Question 2

2a.

1. State Dalton’s law of partial pressure.
2. Identify one type of refrigeration where Dalton’s law of partial pressure is applied.

 

b.    State one difference between the following:

(i)	absolute pressure	vacuum pressure
(ii)	sensible heat	latent hea
(iii)	dry-bulb temperature	wet-bulb temperature

 

c.    A compressor in a refrigerator is rated at 300W. How much electrical energy is used in 20 minutes?

Observation

Question 2c required candidates to calculate much electrical energy is used in 20 minutes for a refrigerated rated 300 W. The expected response is:

Question 3

a.    State four properties of a good refrigerant.
b.    State the reason why Freon gas is banned for use as a refrigerant.
c.    List five tools required to service a window air-conditioner.

Observation

(3) Question 4c required the candidates to convert 500C to Fahrenheit. The expected response is:

Question 4

a.    State three properties of a good insulation material.
b.    State three factors that affect leakage in a cold store.
c.    Convert 50^oC to degree Fahrenheit.

Observation

Question 4c required the candidates to convert 500C to Fahrenheit. The expected response is:

Question 5

a.    State four factors that affects the rate of turnover in an airconditioning and refrigeration business.
b.    Explain the term retained earnings.
c.    The value of a window air conditioner in 2004 was N 40,000. Calculate the value of the air conditioner after it has been used for five years, if it depreciated at 5% annually.

General Comments

The paper was adjudged to be of the required standard and the questions covered a large area of the syllabus. The performance of the candidates generally above average, the highest score being 47/60 this was one mark below that of the previous year.

The candidates performed better in the previous year compared to this year.

The candidates responded well to each of all the questions as all the questions were attempted by the various candidates.

Weakness and Remedies

The students who attempted questions in sketches were poor in drawing. Students also did not do well in the calculation aspects of the questions.

(2)        SUGGESTED REMEDIES FOR OVERCOMING WEAKNESSES

The teachers should endeavor to teach the students drawings related to the trade, the should be advised to attend Technical Drawing classes. The teaches should also practice relevant calculation problems with the students.

Candidates’ Strength

The students performed well in theoretical questions.