Physics Questions and Answers - Form 2 Term 1 Opener Exams 2022

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PHYSICS

INSTRUCTIONS.

  • Answer all the questions in the spaces provided.


Questions

  1. List two career opportunities in physics. (2mks)
  2. Match the following basic physical quantities. (5mks)
    Basic physical quantity SI unit Symbol
    Time Second  
    Electric current   A
    Amount of substance   mol
    Thermodynamic temperature    
  3. Give three differences between mass and weight. (3mks)
  4. A wire of radius 3.0mm and length 200m is melted into a sphere. Calculate the radius of the sphere in metres. (3mks)
  5.        
    1. Give two precautions necessary while handling a density bottle. (2mks)
    2. 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)
  6. 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)
  7. Define force and state its SI Unit. (2mks)
  8. 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)
  9. Give two factors affecting surface tension. (2mks)
  10. Describe the working mechanism of a hydraulic brake system. (4mks)
  11. The figure below shows a U-tube filled with water, mercury and another liquid, determine the density of the liquid. (3mks)
    F2ot105pycQ11
  12. 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.
    F2ot105pycQ12
    1. State which gas diffused faster. (1mk)
    2. Explain how the rate of diffusion depends on the density of a gas. (2mks)
    3. Explain the effect of performing the experiment above at a higher temperature. (2mks)
  13. 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)
  14. What is the purpose of a translucent screen on the:
    1. Pinhole camera. (1mk)
    2. Give two characteristics of image formed by a pinhole camera. (2mks)
    3. 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)
  15. State the laws of reflection. (2mks)
    1. Angle of incidence (2mks)
    2. Give three characteristics of the images formed by a plane mirror. (3mks)
    3. How many images would be seen from two mirrors when reflecting surfaces make an angle of 60° with each other? (2mks)
    4. A plane mirror is suspended using a string and makes an angle of 35° with the wall as shown below,
      F2ot105pycQ15d
      A ray of light strikes the mirror horizontally. Calculate the angle between the horizontal and the reflected ray. (3mks)
  16.        
    1. State the basic law of electrostatic charges. (1mk)
    2. List three uses of the electroscope. (3mks)
    3. List down the hazards of electrostatics. (2mks)
  17.    
    1. Define electric current. (1mk)
    2. A charge of 180 coulombs flows through a lamp:
      1. Every minute. Calculate the current flowing through the lamp. (2mks)
      2. Calculate the number of electrons involved (charge of electron is 1.6 x 10-19C) (3mks)


Marking Scheme

  1. List two career opportunities in physics. (2mks)
    • Bachelor of medicine
    • Bachelor of Architecture
  2. 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
  3. 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.

  4. 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

  5. Give two precautions necessary while handling a density.
    1. Bottle (2mks)
      • The outside of the bottle must be wiped carefully.
      • Ensure no air bubbles when bottle is filled with liquid.

    2. 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

  6. 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

  7. Define force and state its SI Unit. (2mks)
    • Force us a push or a pull
    • S.I unit Newtons

  8. 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.

  9. Give two factors affecting surface tension. (2mks)
    • Impurities
    • Temperature

  10. 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.

  11. 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/mx1000/kg
      = 2500N/m2
      Pl=hpg
      = 0.22 x p x 10
      = 2.2p
        2500   2.2p  
          2.2          2.2
      P=1136.36kg/m3

  12. 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.
    1. State which gas diffused faster. (1mk)
      • Ammonia gas

    2. 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.

    3. 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.

  13. 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)
      L- l0=L0α(t2-t0)
      L2= 10+10x0.08 (20-0)
      Reading = 26°C

  14. What is the purpose of a translucent screen on the:
    1. Pinhole camera. (1mk)
      • This is where the image forms.

    2. Give two characteristics of image formed by a pinhole camera. (2mks)
      • Image is inverted
      • Image is real

    3. 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

  15. State the laws of reflection. (2mks)
    1. 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.

    2. 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.

    3. 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

    4. A plane mirror is suspended using a string and makes an angle of 35O with the wall as shown below,
    5. A ray of light strikes the mirror horizontally. Calculate the angle between the horizontal and the reflected ray. (3mks)
      • Ѳ=35°+35°
      • =70°

  16.                  
    1. State the basic law of electrostatic charges. (1mk)
      • Like charges repel and unlike charges attract each other.

    2. 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.

    3. List down the hazards of electrostatics. (2mks)
      • Sparks and fires
      • Electric shock
      • Lightening

  17.         
    1. Define electric current. (1mk)
    2. A charge of 180 coulombs flows through a lamp:
      • Electric current – rate of flow of charge.

    3. Every minute. Calculate the current flowing through the lamp. (2mks)
      1.      
        • Q =180C
        • T= 1 minute
        • I = Q/t =180/60 =3A

      2. 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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