Free KCSE Physics Topical Questions KNEC Standards

K.C.S.E Physics Q & A - MODEL 2019PP1QN18

31/7/2020

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K.C.S.E Physics Q & A - MODEL 2019PP1QN18

(a) Figure 9 shows a graph of pressure against temperature for a fixed mass of gas at constant volume.

From the graph, determine the values of n arid e given that P = nT + c where n and c are constants.
(b) Explain why it is not possible to obtain zero pressure of a gas in real life situation.
(c) A fixed mass of a gas occupies 1.5 X 10^-3 m^-3 at a pressure of 760 mmHg and a temperature of 273 K. Determine the volume the gas will occupy at a temperature of 290K and a pressure of 720 mmHg.
(d) State any three assumptions made in kinetic theory of gases.

answers

(b) It is not possible to reduce the pressure of a gas to zero since by then most of the temperatures are very low hence the gas liquefies.

(d) Assumptions of the kinetic theory of gases:
Attraction of between the molecules is negligible.
Volume of the molecule is negligible compared to the volume of the container occupied by the gas.
The molecules undergo elastic collisions.
The length of time of a collision is negligible compared to the time between collisions.

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K.C.S.E Physics Q & A - MODEL 2018PP1QN18

29/7/2020

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K.C.S.E Physics Q & A - MODEL 2018PP1QN18

(a) State two quantities that must be kept constant in order to verify Boyle’s law.
(b) An air bubble at the bottom of a beaker full of water becomes larger as it rises to the surface. State the reason why;
(i) the bubble rises to the surface,
(ii) It becomes larger as it rises.
(c) State two assumptions made in explaining the gas laws using the kinetic theory of gases.
(d) Figure 11 shows an incomplete experimental set up that was prepared by a student to verify one of the gas laws.

(i) State with a reason which one of the laws may be verified using the set up.
(ii) State what the student left out in the diagram of the set up.
(c) The volume of a fixed mass of a gas reduced from 500 cm³ to 300 cm³ at constant pressure. The initial temperature was 90K. Determine the final temperature

answers

(a) Mass
Temperature
(b)(i) The gas is less dense than the water.
(ii) As it rises the pressure around the bubble reduces and since the temperature is the same, the volume increases.
(c) The size of the molecules is assumed to be negligible.
Intermolecular forces are also assumed to be negligible.
Real gases can never have zero volume yet the gas laws assume presence of zero volume.
(d)(i) The pressure law.
Has ability to measure the temperature and the pressure while keeping the volume constant.
(ii) Source of heating for the temperature to be changed.

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K.C.S.E Physics Q & A - MODEL 2018PP1QN10

28/7/2020

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K.C.S.E Physics Q & A - MODEL 2018PP1QN10

Figure 6 Shows the relationsh1 between Volume and pressure for a certain gas.

Name the law that the gas obeys.

answer

Boy1e’s law.

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State one assumption for the experiments carried out to verify the gas laws.

28/7/2020

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K.C.S.E Physics Q & A - MODEL 2017PP1QN10

State one assumption for the experiments carried out to verify the gas laws.

answer

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K.C.S.E Physics Q & A - MODEL 2016PP1QN15

27/7/2020

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K.C.S.E Physics Q & A - MODEL 2016PP1QN15

(a) State what is meant by an ideal gas
(b) The pressure acting on a gas in a container was changed steadily while the temperature of the gas maintained constant. The value of volume V of the gas was measured for various values of pressure. The graph in figure 11 shows the relation between the pressure, p and the reciprocal of volume 1/v

(i) Suggest how the temperature of the gas could be kept constant
(ii) Given that the relation between the pressure P1 and the volume, V₁ of the gas is given by PV = k, where k is a constant, use the graph to determine the value of k.
(iii) What physical quantity does k represent?
(iv)State one precaution you would take when performing such an experiment
(c) A gas occupies a volume of 4000 litres at a temperature of 37⁰C and normal atmospheric pressure. Determine the new volume of the gas if it is heated at constant pressure to a temperature of 67⁰C (normal atmospheric pressure P= 1.01 x 10⁵ pa)

answers

(a)A gas that obeys the gas laws perfectly
(b) (i)By changing pressure very slowly or by allowing gas to go to original temperature after each change

(iii)Work done on the gas
(iv)Use dry gas
Make very small changes in pressure

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FORM I - PHYSICS SYLLABUS

Introduction to Physics (4 Lessons)
Measurements 1 (12 Lessons)
Force (16 Lessons)
Pressure (24 Lessons)
Particulate Nature of Matter (12 Lessons)
Thermal Expansion (12 Lessons)
Heat Transfer
Rectilinear Propagation of Light and Reflection at Plane Surface (16 Lessons)
Electrostatics (12 Lessons)
Cells and Simple Circuits (12 Lessons)

FORM II - PHYSICS SYLLABUS

Magnetism (12 Lessons)
Measurements II (16 Lessons)
Turning Effect of Force (10 Lessons)
Equilibrium Centre of Gravity (12 Lessons)
Reflection at Curved Surfaces (16 Lessons)
Magnetic Effect of Electric Current (18 Lessons)
Hooke's Law (8 Lessons)
Waves (14 Lessons)
Sound (12 Lessons)
Fluid Flow (14 Lessons)

FORM III - PHYSICS SYLLABUS

Linear Motion (20 Lessons)
Refraction of Light (20 Lessons)
Laws of Motion (15 Lessons)
Energy, Power and Machines (20 Lessons)
Current Electricity (20 Lessons)
Waves II(10 Lessons)
Electrostatics II (15 Lessons)
Heating Effect of Electric Current (10 Lessons)
Quantity of Heat (20 Lessons)
Gas Laws (15 Lessons)

FORM IV - PHYSICS SYLLABUS

Thin Lenses (20 Lessons)
Uniform Circular Motion (10 Lessons)
Floating and Sinking (15 Lessons)
Electromagnetic Spectrum (15 Lessons)
Electromagnetic Induction (20 Lessons)
Mains Electricity (10 Lessons)
Cathode Rays and Cathode Ray Tube (10 Lessons)
X-rays (8 Lessons)
Photoelectric Effect (15 Lessons)
Radioactivity (15 Lessons)
Electronics (10 Lessons)

K.C.S.E Physics Q & A - MODEL 2019PP1QN18

K.C.S.E Physics Q & A - MODEL 2019PP1QN18

K.C.S.E Physics Q & A - MODEL 2018PP1QN18

K.C.S.E Physics Q & A - MODEL 2018PP1QN18

K.C.S.E Physics Q & A - MODEL 2018PP1QN10

K.C.S.E Physics Q & A - MODEL 2018PP1QN10

State one assumption for the experiments carried out to verify the gas laws.

State one assumption for the experiments carried out to verify the gas laws.

K.C.S.E Physics Q & A - MODEL 2016PP1QN15

K.C.S.E Physics Q & A - MODEL 2016PP1QN15

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FORM I - PHYSICS SYLLABUS

FORM II - PHYSICS SYLLABUS

FORM III - PHYSICS SYLLABUS

FORM IV - PHYSICS SYLLABUS

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