PHYSICS
INSTRUCTIONS.
- Answer all the questions in the spaces provided.
Questions
- List two career opportunities in physics. (2mks)
- Match the following basic physical quantities. (5mks)
Basic physical quantity SI unit Symbol Time Second Electric current A Amount of substance mol Thermodynamic temperature - Give three differences between mass and weight. (3mks)
- A wire of radius 3.0mm and length 200m is melted into a sphere. Calculate the radius of the sphere in metres. (3mks)
-
- Give two precautions necessary while handling a density bottle. (2mks)
- The mass of an empty density bottle is 20g. its mass when filled with water is 40g and 50g when filled with liquid X. calculate the density of liquid X if the density of water is 1000Kgm-3.(3mks)
- 1800cm3 of fresh water of density 1000kg/m3 is mixed with 2200cm3 of sea water of density 1025kg/m3. Calculate the density of the mixture. (3mks)
- Define force and state its SI Unit. (2mks)
- Explain why water rises up in narrow tubes but mercury, which is also a liquid, falls in narrow tubes to a level below the outside surface. (2mks)
- Give two factors affecting surface tension. (2mks)
- Describe the working mechanism of a hydraulic brake system. (4mks)
- The figure below shows a U-tube filled with water, mercury and another liquid, determine the density of the liquid. (3mks)
- The figure below, ammonia gas and an acid gas diffuse and react to form a white deposit on the walls of the glass tube, the deposit forms nearer end B.
- State which gas diffused faster. (1mk)
- Explain how the rate of diffusion depends on the density of a gas. (2mks)
- Explain the effect of performing the experiment above at a higher temperature. (2mks)
- A faulty mercury thermometer reads 10°C when dipped into melting ice and 90°C when on steam at normal atmospheric pressure. Determine the reading of this thermometer when dipped into a liquid at 20°C. (3mks)
- What is the purpose of a translucent screen on the:
- Pinhole camera. (1mk)
- Give two characteristics of image formed by a pinhole camera. (2mks)
- The distance between the pinhole and screen of a pinhole camera is 10cm. the height of the screen is 20cm. at what minimum distance from the pinhole must a man 1.6m tall stand if a full length image is required? (3mks)
- State the laws of reflection. (2mks)
- Angle of incidence (2mks)
- Give three characteristics of the images formed by a plane mirror. (3mks)
- How many images would be seen from two mirrors when reflecting surfaces make an angle of 60° with each other? (2mks)
- A plane mirror is suspended using a string and makes an angle of 35° with the wall as shown below,
A ray of light strikes the mirror horizontally. Calculate the angle between the horizontal and the reflected ray. (3mks)
-
- State the basic law of electrostatic charges. (1mk)
- List three uses of the electroscope. (3mks)
- List down the hazards of electrostatics. (2mks)
-
- Define electric current. (1mk)
- A charge of 180 coulombs flows through a lamp:
- Every minute. Calculate the current flowing through the lamp. (2mks)
- Calculate the number of electrons involved (charge of electron is 1.6 x 10-19C) (3mks)
Marking Scheme
- List two career opportunities in physics. (2mks)
- Bachelor of medicine
- Bachelor of Architecture
- Match the following basic physical quantities. (5mks)
Basic physical quantity SI unit Symbol Time Second s Electric current Ampere A Amount of substance Mole mol Thermodynamic temperature Kelvin k - Give three differences between mass and weight. (3mks)
- Mass is quantity of matter in a body while weight is pull of gravity on a body.
- Mass is measured in kilograms while weight is measured in Newtons.
- Mass is same everywhere while weight changes from place to place.
- A wire of radius 3.0mm and length 200m is melted into a sphere. Calculate the radius of the sphere in metres. (3mks)
- R = 0.003
V=ûr2h
= 22/7 x 0.0032x200
=0.00566m3
V=4/3πr3
0.00566 x ¾ x 7/22=r3
r3=0.00135
r=0.1105m
- R = 0.003
- Give two precautions necessary while handling a density.
- Bottle (2mks)
- The outside of the bottle must be wiped carefully.
- Ensure no air bubbles when bottle is filled with liquid.
- The mass of an empty density bottle is 20g. its mass when filled with water is 40g and 50g when filled with liquid X. calculate the density of liquid X if the density of water is 1000Kgm-3. (3mks)
- water = 40-20=20g
p=1g/cm3
volume = 20g=20cm3
1g/cm3
=20cm3
Mass liquid 50-20=30g
P=m/v =30/20= 1.5g/cm3
- water = 40-20=20g
- Bottle (2mks)
- 1800cm3 of fresh water of density 1000kg/m3 is mixed with 2200cm3 of sea water of density 1025kg/m3. Calculate the density of the mixture. (3mks)
- Mass of fresh water =PV
=1800 x1
=1800g
Sea water m=PV
=2200x1.025
=2255g
dm.= m.m
v.m
= 1800 + 2255
1800+2200
= 4055
4000
=1.01375 g/cm3
- Mass of fresh water =PV
- Define force and state its SI Unit. (2mks)
- Force us a push or a pull
- S.I unit Newtons
- Explain why water rises up in narrow tubes but mercury, which is also a liquid, falls in narrow tubes to a level below the outside surface. (2mks)
- Adhesive force between water and glass molecules is greater than cohesive forces hence water rises.
- Force of cohesion within mercury is grater than adhesive force between mercury and glass.
- Give two factors affecting surface tension. (2mks)
- Impurities
- Temperature
- Describe the working mechanism of a hydraulic brake system. (4mks)
- Force applied on brake pedal excerts pressure on master cylinder.
- The pressure is transmitted by the brake fluid to the slave cylinder. This opens the piston and brake shoe hence brake lining press the drum hence motion is resited.
- The figure below shows a U-tube filled with water, mercury and another liquid, determine the density of the liquid. (3mks)
- Pw=hpg
= 0.25m x 1000kg/m3 x1000/kg
= 2500N/m2
Pl=hpg
= 0.22 x p x 10
= 2.2p
2500 = 2.2p
2.2 2.2
P=1136.36kg/m3
- Pw=hpg
- The figure below, ammonia gas and an acid gas diffuse and react to form a white deposit on the walls of the glass tube, the deposit forms nearer end B.
- State which gas diffused faster. (1mk)
- Ammonia gas
- Ammonia gas
- Explain how the rate of diffusion depends on the density of a gas. (2mks)
- The denser the heavier the particles and hence the slower the gas.
- The denser the heavier the particles and hence the slower the gas.
- Explain the effect of performing the experiment above at a higher temperature. (2mks)
- The rate at which Ammonia gas travels towards B will be higher hence less time taken to form the white deposit.
- The rate at which Ammonia gas travels towards B will be higher hence less time taken to form the white deposit.
- State which gas diffused faster. (1mk)
- A faulty mercury thermometer reads 10°C when dipped into melting ice and 90°C when on steam at normal atmospheric pressure. Determine the reading of this thermometer when dipped into a liquid at 20°C. (3mks)
- 90-10=0.08k-1 =0.08K-1
10(100-0)
L2 - l0=L0α(t2-t0)
L2= 10+10x0.08 (20-0)
Reading = 26°C
- 90-10=0.08k-1 =0.08K-1
- What is the purpose of a translucent screen on the:
- Pinhole camera. (1mk)
- This is where the image forms.
- This is where the image forms.
- Give two characteristics of image formed by a pinhole camera. (2mks)
- Image is inverted
- Image is real
- The distance between the pinhole and screen of a pinhole camera is 10cm. the height of the screen is 20cm. at what minimum distance from the pinhole must a man 1.6m tall stand if a full length image is required? (3mks)
- h1= 0.2m
h0=1.6m
v= 0.1m
u=?
u=h₀ x v
h1
=1.6 x 0.1
0.2
= 0.8m
- h1= 0.2m
- Pinhole camera. (1mk)
- State the laws of reflection. (2mks)
- Angle of incidence (2mks)
- Equals the angle of reflection. Incident ray, reflected ray and normal at point of incidence all lie on the same plane.
- Equals the angle of reflection. Incident ray, reflected ray and normal at point of incidence all lie on the same plane.
- Give three characteristics of the images formed by a plane mirror. (3mks)
- Image is same size as the object.
- Image is far behind the mirror as object is infront of the mirror.
- Image is virtual, erect and laterally inverted.
- How many images would be seen from two mirrors when reflecting surfaces make an angle of 60O with each other? (2mks)
- N= 360°-1
Ѳ
= 360°-1
Ѳ
=5
- N= 360°-1
- A plane mirror is suspended using a string and makes an angle of 35O with the wall as shown below,
- A ray of light strikes the mirror horizontally. Calculate the angle between the horizontal and the reflected ray. (3mks)
- Ѳ=35°+35°
- =70°
- Angle of incidence (2mks)
-
- State the basic law of electrostatic charges. (1mk)
- Like charges repel and unlike charges attract each other.
- Like charges repel and unlike charges attract each other.
- List three uses of the electroscope. (3mks)
- To defect the presence of charge on a body.
- To test the sign of charge on a charged body.
- To test the quantity of charge on a charged body.
- List down the hazards of electrostatics. (2mks)
- Sparks and fires
- Electric shock
- Lightening
- State the basic law of electrostatic charges. (1mk)
-
- Define electric current. (1mk)
- A charge of 180 coulombs flows through a lamp:
- Electric current – rate of flow of charge.
- Electric current – rate of flow of charge.
- Every minute. Calculate the current flowing through the lamp. (2mks)
-
- Q =180C
- T= 1 minute
- I = Q/t =180/60 =3A
- Calculate the number of electrons involved (charge of electron is 1.6 x 10-19C) (3mks)
- He=Q
- Q=IT
- he=it
n x 1.6 x 10-19 = 3 x 60
1.6x10-19 1.6x10-19 - h= 1.25 x 1021 electrons
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