Physics Questions and Answers - Form 4 Mid Term 2 Exams 2023

QUESTIONS

1. Explain why gases is faster in gases compared to liquids. (2mk)
2. A needle may float on clean water but sinks when a detergent is added. Explain. (1mk)
3. A body is projected vertically upwards from the top of the building. Assuming that it lands on the base of the building. Sketch the velocity time graph of the motion. (2mks)
4. State a reason why an air bubble increase in volume as it rises up the surface in a boiler. (1mk)
5. Explain why electric kettle with shiny out surface is more efficient compared to the dull kettle. (1mk)
6. Distinguish between real and virtual image. (1mk)
7. A pinhole camera forms an image of size 10cm. The object is 5M tail and 20m away from the pinhole. Find the length of the pinhole camera. (2mks)
8. Define the term principal focus for diverging lens. (1mk)
9. State any two factors that determine the heating effect by an electric current. (2mks)
10. Arrange the following in descending order of wave lengths. Infrared, X-rays, Gamma rays, micro waves and ultra violet.  (2mks)
11. Explain the difference between soft and hard X rays. (2mks)
12.                    
    1. State the law of floatation. (1mk)
    2. Explain one way of destroying a magnet. (2mks)
13. State two factors that determine the capacitance of a parallel plate capacitor.
14. The figure below shows four capacitors connected to a battery of 12 volts.
    
    
    1. Calculate the effective capacitance.  (3mks)
    2. Charge on 3.2 µ∫ capacitor. (2mks)
    3. P.d across µ∫ capacitor. (2mks)
    4. Energy stored in the 2µ∫. (2mks)
    5. Give one application of capacitors. (1mk)
15. 1. The table below shows the results obtained using different frequencies and their corresponding stopping potentials.
       

       colour	Frequency of x1014 42	Stopping potential V3(V)
       Violet	7.5	1.2
       Blue	6.7	0.88
       Green	6.0	0.60
       Yellow	5.2	2.8
       Orange	4.8	012

       Draw a graph of potential V3 against frequency.  (5mks)
    2. Using the graph to find
       1. Threshold frequency.   (2mks)
       2. Work function.    (2mks)
16.                  
    1. Distinguish between angular and linear velocity. (1mk)
    2. Explain the difference of centripetal force from other force. (1mk)
    3. A stone is whirled with a uniform speed in a horizontal circle having radius of 10cm. It takes the stone 10 seconds to describe an arc of length 4cm. Calculate
       1. Angular velocity (W)         (3MKS)
       2. Linear velocity V of the stone. (3mks)
       3. The period time T (2mks) 

MARKING SCHEME

1. Explain why gases is faster in gases compared to liquids. (2mk)
   • They have lower intermolecular force compared to liquid
   • They posses high kinetic energy compared to liquids
   • The molecules are far apart each other compared to the liquid
2. A needle may float on clean water but sinks when a detergent is added. Explain. (1mk)
   • clean water has compact surface tension hence the needle floats when the detergent is added it breaks the surface tension hence the needle sinks
3. A body is projected vertically upwards from the top of the building. Assuming that it lands on the base of the building. Sketch the velocity time graph of the motion. (2mks)
   • corect diagram
4. State a reason why an air bubble increase in volume as it rises up the surface in a boiler. (1mk)
   • as a bubble rises the pressure reduces and the volume increases
5. Explain why electric kettle with shiny out surface is more efficient compared to the dull kettle. (1mk)
   • shinny surfaces reduce the heat less through radiation since they are heat emmitters unlike the dull objects which are absorbers
6. Distinguish between real and virtual image. (1mk)
   • real is formed by the intersection of the real rays whereas the virtual image is formed by intersection of virtual rays
7. A pinhole camera forms an image of size 10cm. The object is 5M tail and 20m away from the pinhole. Find the length of the pinhole camera. (2mks)
8. Define the term principal focus for diverging lens. (1mk)
   • This is a point at which rays (lose to and parallel to the principal axis seems to diverge from after striking the lens
9. State any two factors that determine the heating effect by an electric current. (2mks)
   • resistance
   • Time of handling
   • current supplied
10. Arrange the following in descending order of wave lengths. Infrared, X-rays, Gamma rays, micro waves and ultra violet.  (2mks)
    • Microwaves, infrared, ultraviolet, xrays, gamma rays
11. Explain the difference between soft and hard X rays. (2mks)
    • self x rays have low penetration power compared to hard x rays
    • soft srays have relatively / aver velocity compared to hard x rays
12.                    
    1. State the law of floatation. (1mk)
       • A body displaces its own weight of the fluid it floats on
    2. Explain one way of destroying a magnet. (2mks)
       • hammering - west east direction
       • heating
13. State two factors that determine the capacitance of a parallel plate capacitor.
    • distance between the plates
    • Type of the dielatric material used
    • Area of the overlaping plates
14. The figure below shows four capacitors connected to a battery of 12 volts.
    
    
    1. Calculate the effective capacitance.  (3mks)
       • 1/2 + 1/8 = 5/8
         5/8 = 8/5 = 1.6
         1 - 6 + 3.2 = 4.8
         1/5 + 1/4.8 
         = 49/120
         = 2.45 uf
    2. Charge on 3.2 µ∫ capacitor. (2mks)
       • charge = Cv
         =3.2 x 6.12 = 1.9584 x 10^-5
    3. P.d across µ∫ capacitor. (2mks)
       • Q = Cv = 12 x 2.45 x 10^-6 = 2.94 x 10^-5
         v = Q/C
         = 2.94 x 10^-5
             5 x 10^-6
         = 5.88V
    4. Energy stored in the 2µ∫. (2mks)
       • E = 1/2CV2 = 1/2 Qv = 1/2 x 2uf x 10^-6 x 5.88 x 5.88 
         = 3.45 x 10^-5 J
    5. Give one application of capacitors. (1mk)
15. 1. The table below shows the results obtained using different frequencies and their corresponding stopping potentials.
       

       colour	Frequency of x1014 42	Stopping potential V3(V)
       Violet	7.5	1.2
       Blue	6.7	0.88
       Green	6.0	0.60
       Yellow	5.2	2.8
       Orange	4.8	012

       Draw a graph of potential V3 against frequency.  (5mks)
       
    2. Using the graph to find
       1. Threshold frequency.   (2mks)
          • 4.5 x 10¹⁴ H2
       2. Work function.    (2mks)
          • 72 x 0.025 = 1.8 x 1.6 x 10^-19
            2.88 x 10^-19 J
16.                  
    1. Distinguish between angular and linear velocity. (1mk)
       • Angular velocity is the rate change in angular displacement per time whereas linear velocity is the rate change in linear displacement per time
    2. Explain the difference of centripetal force from other force. (1mk)
       • centripetal force the force which keeps the body in a creat or motion by attracting it towards the centre of the circle
    3. A stone is whirled with a uniform speed in a horizontal circle having radius of 10cm. It takes the stone 10 seconds to describe an arc of length 4cm. Calculate
       1. Angular velocity (W)         (3MKS)
          • Angular velocity = angular displacement/time
            0.04 m / 0.1
            = 0.4/10 = 0.04
       2. Linear velocity V of the stone. (3mks)
          • linear velocity = angular velocity x radius 
            = 0.04 x 0.1 
            4 x 10^-3 m/s
       3. The period time T (2mks)
          • period = 2πr
                            v
            T = 2 x 22/7 x 0.1 = 157.142 seconds
                   4.0 x 10^-3