Physics Questions and Answers - Form 2 Term 3 Opener Exams 2022

INSTRUCTION TO CANDIDATES

• Answer ALL the questions in both Section A and B in the spaces provided.
• ALL working MUST be clearly shown.
• Candidates should answer the questions in English
• Where necessary, take
  G = 10N/kg
  Density of water = 1000kg/m3

SECTION A (25 MARKS)

Answer all questions in the spaces provided

1. The figure below shows a scale which is part of vernier calipers. What is the reading indicated by the scale? (2mks)
   
2. Two mirrored walls stand at an angle to each other. A student standing in the room counts nine images of himself in the mirrors. Determine the angle between the walls   (3mks)
3. The diagram below shows the behavior of mercury in a capillary tube. Explain this observation (2mks)
   
4. A body weighs 600N on the surface of the earth and 450N on the surface of another planet. Calculate the value of g in that planet (g on the earth = 10N/Kg) (3mks)
5. A steel needle when placed carefully on water can be made to float. When a detergent is added to the water it sinks. Explain this observation (2mks)
6. 200 coulombs of charge passes through a point in a circuit for 0.6 minutes. What is the magnitude of the current flowing? (3mks)
7. When marking the fixed points on a thermometer it is observed that at 00C, the mercury thread is of length 1cm and 6cm at 1000C. What temperature would correspond to a length of 4cm? (3mks)
8. The micrometer screw gauge below has a zero error of −0.19mm.
   
   Determine the actual thickness of the object. (2mks)
9. Distinguish between hard magnetic material and a soft magnetic material (2mks)
10. In the smoke cell experiment, bright specks are observed to move in a continuous random manner. Explain this motion. (2mks)
11. State the reason why a steel sphere resting on a horizontal surface is said to be in neutral equilibrium (1mk)

SECTION B (55 MARKS)

12.  
    1. State Hooke’s law (1mk)
    2. In an experiment to verify Hooke’s law, a piece of rubber was fixed to a rigid support and the other end pulled with a force of ranging magnitude. The values of force and the extension were recorded as in the table below:-
       

       Force (N)	0	0.20	0.55	0.75	1.00	1.30	1.40
       Extension(cm)	0	1.5	2.5	3.5	4.5	6.0	7.0

       1. Plot a graph of force ( Y axis) against extension (X-axis) on the gird provided     (5mks)
       2. From the graph, determine the spring constant of the rubber within elastic limit  (3mks)
       3. What is the size of force at the elastic limit (2mks)
    3. Three identical springs A, B and C of negligible weight are connected as shown below:
       
       The springs support a load of 60N. If the spring constant of each is 150N/m, determine the total extension of the springs (3mks)
13.  
    1. State the Pascal’s principle (1mk)
    2. The height of a mercury barometer at a particular place is 70cm. given that the density of mercury is 13600kgm³, determine;
       1. The atmospheric pressure at the place. (3mks)
       2. The height of a water barometer at the same place. (Density of water=1g/cm³) (2mks)
       3. Give a reason why mercury is preferred as a barometric liquid. (1mks)
    3. Calculate the minimum pressure a block of dimensions 3cm*10cm*15cm and mass 12kg could exert on a horizontal surface. (3mks)
14.  
    1. In an experiment to determine the diameter of an oil molecule, an oil drop of radius 0.02cm was placed in a tray of water in which lycopodium powder had been sprinkled oil drop spread to a circular patch of radius of 0.2cm.
       Determine:
       1. The volume of the oil drop (2mks)
       2. The area of the patch (2mks)
       3. Diameter of the oil molecule (3mks)
    2. state two assumptions made in the experiment above. (2mks)
15.  
    1. What property of light is suggested by the formation of shadows? (1mk)
    2. A building standing 200m from a pinhole camera produces on the screen of the camera an image 2.5cm high 5.0cm behind the pinhole.
       Determine the actual height of the building (3mks)
    3. An object of height 2.0cm is placed 5.0cm in front of a convex mirror of focal length 10.0cm
       1. On the grid provided,draw to scale a ray diagram to locate the position of the image.(4mks)
       2. Calculate the magnification produced by the mirror. (2mks)
16.  
    1. State the principle of moments (1mk)
    2. The figure below shows a uniform metre rule of mass 300g acted upon by a number of forces.
       
       Determine;
       1. Sum of clockwise moments(leave your answer in terms of W) (2mks)
       2. Sum of anticlockwise moments (2mks)
       3. The force W (2mks)
17. The figure below shows an electromagnet
    
    
    1. Explain why the cord is made up of iron and not steel (2mks)
    2. On the same diagram indicate the direction of the current flow when the switch is closed (1mk)
    3. When current is allowed to flow, the electromagnet becomes magnetized.
       Identify the poles of the magnet (2mks)
       1. __________________________________
       2. ___________________________________
    4. State three factors that affect the strength of the electromagnet (3mks)

MARKING SCHEME

1. M.S.R. = 3.90
   V.S.R. = 0.06
   Reading = 3.96cm
2. n = 360 1
            θ
   9= 360  1
           θ
   θ= 360   1
         10
       =36°
3. The force of cohesion within the mercury is greater than the force of adhesion between mercury and glass. The mercury therefore sinks down the tube to enable mercury molecules to keep together.
4. Mass on the earth’s surface = 600
                                                    10
                                                = 60Kg
   Value of g in the other planet = 450
                                                      60
                                                  = 7.5N/Kg
5. The steel needle floats due to surface tension of water. The detergent which is an impurity breaks the surface tension hence the needle sinks
6. Q=It
   200=I × 0.6 × 60
     I= ²⁰⁰/₃₆ 
     =5.556A
7.  
   
   5cm = 100°C
   1cm = 100 x 1
                    5
          = 20°C
   Therefore, a length of 4cm corresponds to a temp. of 60°C
8. Reading shown is
      3.50
   + 0.01
      3.51mm
   Actual thickness = 3.51
                              + 0.19
                                 3.70mm
9. Hard Magnetic materials are materials that are difficult to magnetise but once magnetized, they retain their magnetism for long, while soft magnetic materials are materials that are easily magnetized but do not retain their magnetism for long.
10. This is because of the uneven bombardment of the smpke particles with the invisible air particles which are in continuous random motion.
11. Its center of gravity does not change.
12.  
    1. For a helical spring or other elastic material, the extension is directly proportional to the stretching force, provided elastic limit is not exceeded.
    2.  
       1. A GRAPH OF FORCE AGAINST EXTENSION
          
          
          
       2. K = ΔF
                 ΔE
          = 0.75 - 0.2
              3.5 - 1.0
          = 0.5
             2.5
          = 0.2N/cm
       3. 1.3 N
    3. Combined spring constant for A and B
       = 150 x 2
       = 300N/m
       Extension produced by A and B
       ⁶⁰/₃₀₀
       = 0.2m
       Extension produced by C = ⁶⁰/₁₅₀ 
                                                = 0.4m
       Total extension = 0.2 + 0.4
                                = 0.6m
13.  
    1. Pressure applied at one part in a liquid is transmitted equally to all other parts of the enclosed liquid.
    2.  
       1. Pa = 0.7×13600×10
               =95200N/m²
       2. 95200=h×1000×10
          h =    95200   
                (1000×10)
             =9.52m
       3. Mercury is much denser than water.
    3. Pmin =   120 
                     0.15
                =8000N/m²
14.  
    1.  
       1. V = ⁴/₃ πR³
             = ⁴/₃  x 3.142 x 0.02³
            = 0.0335cm³
       2. A =πr²
              = 3.142 x 0.2²
               = 0.125cm²
       3. d = ^V/_A
          = 0.0335
              0.1256
          = 0.2667cm
    2. The oil drop is a perfect sphere
       The oil drop is one molecule thick
15.  
    1. Light travels in a straight line
    2. hi = v
       ho   u
       ho = 2.5 x 20000
                      5
           = 10000cm or 100m
    3.  
       1.  
          
       2. M = ^v/_u
              = ⁸/₅ 
              = 1.6
16.  
    1. For a system in equilibrium, the sum of clockwise moments about a point must be equal to the sum of the anticlockwise moments about the same point
    2.  
       1. (0.6 x W ) + (2.0 x 0.4) = 0.6W+0.8
       2. (0.1 x 3) + (0.3 x 4) = 0.3 + 1.2
                                          = 1.5 N/m
       3. 1.5 = 0.6 W + 0.8
          0.6W =  0.7
          W = 0.7 
                  0.6
              =1.1667N
17.  
    1. Iron is a soft magnetic material while steel is a hard magnetic material
    2. Current flow in the anticlockwise direction
    3.  
       • A North pole
       • B South pole
    4.  
       • Size of current
       • Number of turns of the wire
       • Shape of the core
       • Length of the solenoid