Physics Questions and Answers - Form 4 Mid-term Exams Term 1 2022

QUESTIONS

1. Three electric bulbs are connected in series with a battery of two dry cells and a switch. At first the bulbs light brightly.
   1. State a reason why they gradually light (2mks)
2. State two reason why a steel sphere resting on a horizontal surface is said to be neutral (1mk)
3. A horizontal force of 15N is applied on a wooden of mass 2kg placed on a horizontal surface. It causes the block to accelerates at 5m/s². Determine the frictional force between the block and the surface. (3mks)
4. The figure shows two pieces of copper metal A and B of different cross-section area into each other and a piece of paper wrapped tightly around the junction.
   
   It is observed that when the flame is applied around the paper at the function, the side of the paper around the copper labeled A burns first. Explain this observation. (2mks)
5. State the law of floating (1mk)
6. The figure shows a piece of cork held with a tight thread attached to the bottom of a beaker.
   
   
   1. Name the forces that acts on the cork (3mks)
   2. Write an expression showing the relation between the forces
7. When an enclosed cylinder full of gas is exposed to high temperature for some time, the cylinder bursts. Explain what cause the bursting of the cylinder. (2mks)
8. When a stone tied with an inextensible string of length L is whirled in a horizontal circular path it experiences a centripetal force state what provides the centripetal force on the stone (1mk)
   1. A student whirls a stone of mass 0.2kg tied to a string of length of 0.4m in a vertical plane at constant speed of 2 revolution per second (take acceleration due to gravity as 10ms 2
      1. State one force acting on the stone when it is at the highest point (1mk)
      2. Determine angular velocity of the stone (2mks)
      3. Determine the tension in the string when the stone is at the highest point (2mks)
9. Two liquids X and Y have densities 125g/cm³ and 1.5g/cm³ respectively. Calculate the density of the mixture containing 25% of X by mass and the rest being Y. (3mks)
10. The figure shows a log of wood of mass 20kg submerged in water in a pond and held in a position by a string fixed to the bottom of the pond.
    
    Given that the density of water is 1000kg/m3 and that of the wood is 800kg/m3, determine the
    1. Volume of the log (2mks)
    2. Tension of the spring (2mks)
11.                
    1. A broadcasting station processes radio waves of wavelength 800m. Determine their frequency (speed of air is 3 x 10 m/s) (2mks)
    2. Arrange the following electromagnetic waves in the order of decreasing frequency; (1mk)
       Microwaves, Gamma rays, Radiowaves, X-rays
    3. An object of height 10 cm is placed 30 cm from a converging lens of focal length 18cm. Draw array diagram to locate the position of the image formed. (3mks)
    4. From the diagram in part (iii) determine:
       1. Image height; (1mk)
       2. Image distance
    5. Show that the magnifying power of a simple microscope is given by M = ^v\_f – 1 where M is magnification v is image and f is focal length. (3mks)
    6. An object stands before a diverging lens of focal length 24cm at a distance of 12cm. Determine the image distance. (3mks)
12.                    
    1. How can you increase the strength and intensity of X – rays from an X – ray tube (2mks)
    2. Distinguish between mechanical wave and electromagnetic waves. (2mks)
13. Give a reason why a candle flame is blown when a high charged conductor is brought close to it as shown below (3mks)
    
    
    1. State two factors that affect capacities of a capacitor (2mks)

MARKING SCHEME

1. Three electric bulbs are connected in series with a battery of two dry cells and a switch. At first the bulbs light brightly.
   1. State a reason why they gradually light (2mks)
      polarisation increases internal resistance of the cell reducing the flow of current
2. State two reason why a steel sphere resting on a horizontal surface is said to be neutral (1mk)
   The position of the centre of gravity of the steel ball does not change even if it is slightly displaced
3. A horizontal force of 15N is applied on a wooden of mass 2kg placed on a horizontal surface. It causes the block to accelerates at 5m/s². Determine the frictional force between the block and the surface. (3mks)
   f = ma = 2.5 kg × 5 = 12.5N
   friction force = 15 - 12.5
   = 2.5 N
4. The figure shows two pieces of copper metal A and B of different cross-section area into each other and a piece of paper wrapped tightly around the junction.
   
   It is observed that when the flame is applied around the paper at the function, the side of the paper around the copper labeled A burns first. Explain this observation. (2mks)
   The copper A has a small cross-section area and therefore conducts heat at at lower rate than copper B. More heat will be retained around the junction on copper A than copper B to burn the paper.
5. State the law of floating (1mk)
   A floating object displaces its own weight of the fluid in which it floats.
6. The figure shows a piece of cork held with a tight thread attached to the bottom of a beaker.
   
   
   1. Name the forces that acts on the cork (3mks)
      upthrust force
      tension
      weight / gravitational force
   2. Write an expression showing the relation between the forces
      u = w + T
      upthrust  = weight + tension
7. When an enclosed cylinder full of gas is exposed to high temperature for some time, the cylinder bursts. Explain what cause the bursting of the cylinder. (2mks)
   Increased temperature increases the kinetic energy of the gas particle. Th particles then collide more with the walls of the cylinder. Greater collision per unit between the gas particles and the cylinder increases the pressure on the walls making the walls to burst.
8. When a stone tied with an inextensible string of length L is whirled in a horizontal circular path it experiences a centripetal force state what provides the centripetal force on the stone (1mk)
   Tension force on the string.
   1. A student whirls a stone of mass 0.2kg tied to a string of length of 0.4m in a vertical plane at constant speed of 2 revolution per second (take acceleration due to gravity as 10ms²
      1. State one force acting on the stone when it is at the highest point (1mk)
         tension on the string
         the weight of the string
      2. Determine angular velocity of the stone (2mks)
         w = 2πf
         = 2 × 3.14 × 2
         = 12.568 rad's
      3. Determine the tension in the string when the stone is at the highest point (2mks)
         tension at the highest point
         = 0.2 ×(12.568) × 0.4 × 6x × 10
         = 10.636N
9. Two liquids X and Y have densities 125g/cm³ and 1.5g/cm³ respectively. Calculate the density of the mixture containing 25% of X by mass and the rest being Y. (3mks)
   density of mixture = I.M
                                     V.M
   = 100
       70
   = 1.429g/cm³
   liquid × mass
   density 1.25g/cm³
   vol 20cm
   total
   liquid 1/7.5
   1.5gcm³
   50 cm
   20150 = 70cm³
10. The figure shows a log of wood of mass 20kg submerged in water in a pond and held in a position by a string fixed to the bottom of the pond.
    
    Given that the density of water is 1000kg/m3 and that of the wood is 800kg/m3, determine the
    1. Volume of the log (2mks)
       v =   mass of the log   =     20kg     = 0.02m³
             density of the log    800kgm^-3
    2. Tension of the spring Upthrust of the log(2mks)
       upthrust of the log = weight of the liquid displaced
       = 0.025 × 1000 × 10 = 250N
11.                
    1. A broadcasting station processes radio waves of wavelength 800m. Determine their frequency (speed of air is 3 x 10 m/s) (2mks)
       f = c  = 3 ×108 = 0.00375 × 10³Hz
          -1       800
    2. Arrange the following electromagnetic waves in the order of decreasing frequency; (1mk)
       Microwaves, Gamma rays, Radiowaves, X-rays
       Gamma rays, x-rays, microwaves, radio waves
    3. An object of height 10 cm is placed 30 cm from a converging lens of focal length 18cm. Draw array diagram to locate the position of the image formed. (3mks)
       the tension in the string 
       upthrust - weight
       = 250N - 200N
       = 50N
    4. From the diagram in part (iii) determine:
       1. Image height; (1mk)
          15 cm
       2. Image distance
          45 cm
    5. Show that the magnifying power of a simple microscope is given by M = ^v\_f – 1 where M is magnification v is image and f is focal length. (3mks)
       1/5 = 1/v + 1/u
       u/5 = v/v + v/a
       v/5 = 1 + m
       m = v/5 - 1
    6. An object stands before a diverging lens of focal length 24cm at a distance of 12cm. Determine the image distance. (3mks)
12.                    
    1. How can you increase the strength and intensity of X – rays from an X – ray tube (2mks)
       f=  -24
       uf.12
       1/v = -1/24 - 1/12
       = -1 - 2 = -3 = -1
            24      24     8
       v= -8cm = 8 cm
    2. Distinguish between mechanical wave and electromagnetic waves. (2mks)
13. Give a reason why a candle flame is blown when a high charged conductor is brought close to it as shown below (3mks)
    
    
    
    1. State two factors that affect capacities of a capacitor (2mks)
       area of overlap
       distance of separation
       type of dieloric