Important Questions For You!

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hapter 1: Force
Q. 1.. A force is applied on                                                                                                                                 [2M]

  1. a rigid body and
  2. non rigid body.

How does the effect of force differ in the two cases?

Q. 2. Explain the motion of a planet around the Sun in a circular path.                                                                   [2M]

Q. 3. What are                                                                                                                                                  [3M]

  1. Centripetal forces
  2. Centrifugal forces?

Q. 4. State and explain the principle of moments. Draw a diagram to illustrate.                                                      [4M]

Q. 5. A ball is placed near the periphery of a merry-go-round and is tied to its centre. Merry-go-round is rotating about an axis passing through its centre.                                                                                                                                 [4M]

  1. What will be your observation when you are standing outside the merry-go- round? Explain it.
  2. What will be your observation when you are standing at the centre of the merry-go-round? Explain it.

Chapter 2: Work, Energy and Power

Q. 1. A force is applied on a body of mass 20 kg moving with a velocity of 40 ms-1. The body attains a velocity of 50 ms-1 in 2 seconds. Calculate the work done by the body.                                                                                                     [2M]

Q. 2. How is work done by a force measured when the force:                                                                                [2M]

  1. is in the direction of displacement?
  2. is in an angle to the direction of displacement?

Q. 3. An engine can pump 30,000 litres of water to a vertical height of 45 metre in 10 minutes. Calculate the work done by the machine and the power.
(Density of water = 103 kg/m3, 1000 litre = 1 m3, g = 9.8ms-2)                                                                            [3M]


Q. 4. An object 'P' of mass m is lifted from a point A on ground to point B at a height 'h' above the Earth by Rina and Mita, but the path taken for doing it is different by both as shown                                                                                                     [3M]

  1. Calculate the work done in both the situations.
  2. In the above given cases, which force is doing positive work and which one is doing negative work?

Q. 5.                                                                                                                                                                     [4M]

(i) State the energy in the following while in use:

  1. Burning of a candle.
  2. A steam engine.

(ii) On what basis would you classify an energy source as renewable? State two advantages and two limitations of the energy received from the Sun.

Chapter 3: Machines

Q. 1. A type of single pulley is very often used as a machine even though it does not give any mechanical advantage.    [2M]

  1. Name the type of pulley used.
  2. For what purpose is such a pulley used?

Q. 2. Draw a simplified diagram of a lemon crusher, indicting of load and effort.                                                           [2M]
Q. 3. A coolie is pushing a box weighing 1500 N up an inclined plane 7.5 m long on to a platform 2.5 m above the ground. [3M]

  1. Calculate the mechanical advantage of the inclined plane.
  2. Calculate the effort applied by the coolie.


Q. 4. Derive a relationship between the mechanical advantage, the velocity ratio and the efficiency of a machine.           [3M]

Q. 5. A block and tackle pulley system has a velocity ratio of 3.                                                                                   [4M]

  1. Draw a labelled diagram of this system. In your diagram, indicate clearly the points of application and the directions of the load and the effort.
  2. Why should the lower block of this pulley system be of negligible weight?

Chapter 4: Refraction of Light at Plane Surfaces 

Q. 1.                                                                                                                                                                      [2M]

  1. The refractive index of glass with respect to air is 1.5. What is the value of refractive index of air with respect to glass?
  2. A ray of light is incident as a normal ray on the surface of separation of two different mediums. What is the value of the angle of incidence in this case?

Q. 2. What are the necessary conditions for the total internal reflection?                                                                      [2M]

Q. 3.                                                                                                                                                                      [2M]

  1. Can the absolute refractive index of a medium be less than one?
  2. A coin placed at the bottom of a beaker appears to be raised by 4.0 cm. If the refractive index of water is 4/3, find the depth of the water in the beaker.

Q. 4. The refractive index of glass is 1.5. From a point P inside a glass block, draw rays PA, PB and PC incident on that glass-air surface at an angle of 30o, 42o and 60o respectively.                                                                                                 [3M]

  1. In the diagram show the approximate direction of these rays as they emerge out of the block.
  2. What is the angle of refraction for the ray PB?

Q. 5.  A ray of light of wavelength 5400Å suffers refraction from air to glass. Taking aμg = 1.5 , find the wavelength of light in glass.[3M]

Chapter 5: Refraction through a Lens


Q. 1. Riya claims to have obtained an image twice the size of the object with a concave lens. Is she correct? Give a reason for your answer.                                                                                                                                                                 [2M]

Q. 2. A lens forms the image of an object placed at a distance 15 cm from it, at a distance 60 cm in front of it. Find: (i) the focal length, (ii) the magnification, and the nature of image.                                                                                             [2M]

Q. 3. A linear object is placed on the axis of a lens. An image is formed by refraction in the lens. For all positions of the object on the axis of the lens, the position of the image is always between the lens and the object.                                                   [3M]

  1. Name the lens.
  2. Draw a ray diagram to show the formation of the image of an object placed in front of the lens at any position of your choice except infinity.

Q. 4. An object AB is placed between 2F1 and F1 on the principal axis of the convex lens as shown in the diagram below:   [4M]



Copy the diagram and using the rays starting from point A, obtain the image of the object formed by the lens.

Chapter 6: Spectrum

Q. 1.                                                                                                                                                                     [2M]

  1. Name a prism required for obtaining a spectrum of Ultraviolet light.
  2. Name the radiations which can be detected by a thermopile.

Q. 2. Name the radiations:                                                                                                                                      [3M]

  1. That are used for photography at night.
  2. That are used for detection of fracture in bones.
  3. Whose wavelength ranges from 100 Å to 4000 Å (or 10 nm to 400nm).

Q. 3. A type of electromagnetic wave has wavelength50Å                                                                                          [3M]

  1. Name the wave.
  2. What is the speed of the wave in vacuum?
  3. State one use of this type of wave.

Q. 4. A ray of white light is passed through a glass prism and spectrum is obtained on a screen.                                   [3M]

  1. Name the seven colours of the spectrum in order.
  2. Do the colours have the same width in the spectrum?
  3. Which of the colour of the spectrum of white light deviates (i) the most? (ii) the least? 

Q. 5. The diagram shown below shows the path taken by a narrow beam of yellow monochromatic light passing through an equiangular glass prism. Now the yellow light is replaced by a narrow beam of white light incident at the same angle. Draw another diagram to show the passage of the beam through the prism and label it to show the effect of prism on the white light.  [3M]

Chapter 7: Sound

Q. 1.                                                                                                                                                                     [2M]

  1. State the safe limit of sound level in terms of decibel for human hearing.
  2. Name the characteristic of sound in relation to its wave form.

Q. 2. Radar sends a signal to an aeroplane at a distance 45 km away with a speed of 3×108 ms-1. After how long is the signal received back from the aeroplane?                                                                                                                          [2M]

Q. 3.                                                                                                                                                                         [3M]

  1. A man standing between two cliffs produces a sound and hears two successive echoes at intervals of 3 s and 4 s respectively. Calculate the distance between the two cliffs. The speed of sound in the air is 330ms-1.
  2. Why will an echo not be heard when the distance between the source of the sound and the reflecting surface is 10m?


Q. 4.                                                                                                                                                                   [4M]

  1. What is meant by the terms (a) amplitude and (b) frequency of a wave?
  2. Explain why stringed musical instruments, like the guitar, are provided with a hollow box.

Q. 5. In the diagram below, A, B, C, D are four pendulums suspended from the same elastic string PQ. The length of A and C are equal to each other while the length of pendulum B is smaller than that of D. Pendulum A is set in to a mode of vibrations. [4 M]

  1. Name the type of vibrations taking place in pendulums B and D?
  2. What is the state of pendulum C?
  3. State the reason for the type of vibrations in pendulum B and C.

Chapter 1: Force
Q. 1. A force is applied on                                                                                                                                 [2M]

  1. a rigid body and
  2. non rigid body.

How does the effect of force differ in the two cases?

Solution: When force is applied to a non-rigid body, it can change its shape or dimensions and can also produce acceleration. When force is applied to a rigid body, it tends to produce acceleration in the body.

Q. 2. Explain the motion of a planet around the Sun in a circular path.                                                                 [2 M]

Solution: The sun binds the planet to move along the orbit around it by its gravitational force. This attractive force provides the necessary centripetal force which keeps the planet moving along the orbit. Although the speed is constant, the direction of motion is not constant. Thus, this uniform circular motion is said to be accelerated motion as the direction of motion keeps on changing continuously. Also, the centripetal force with the help of which the planet moves around the sun is perpendicular to the direction of motion, and hence, the work done by the planet in moving along the circular path around the sun is zero.

Q. 3. What are                                                                                                                                                 [3M]

  1. Centripetal forces
  2. Centrifugal forces?
Solution: (i) Centripetal force: When a body is moving in a circular path with a uniform speed, its velocity is continuously changing due to a change in its direction. The body thus possesses acceleration, and this acceleration is called centripetal acceleration. The force which produces this acceleration is called centripetal force. It acts along the radius towards the centre of the circular path.

(ii) Centrifugal force: It is a force which comes into play in circular motion. This force is equal and opposite to the centripetal force. It tends to throw the body away from the centre. It is not a real force.

Q. 4. State and explain the principle of moments. Draw a diagram to illustrate.                                                    [4M]

Solution: Principle of moments: According to this principle, in equilibrium, the sum of the anticlockwise moments is equal to the sum of the clockwise moments.

To illustrate the principle, consider a uniform rod of length (d1+d2) resting on a knife edge. Two forces F1 & F2 (such that F1> F2) are applied to its two ends (both in the same downward direction). Since the two forces are unequal, the equilibrium point is not in the middle but towards the larger force F1.



Force F2 tends to turn the rod clockwise, while force F1 tends to turn the rod anticlockwise.
i.e. Clockwise moment = F2 x d2
Anticlockwise moment= F1 x d1
In equilibrium, clockwise moment = Anticlockwise moment
i.e. = F2 x d2 = F1 x d1
This illustrates the principle of moments.

Q. 5. A ball is placed near the periphery of a merry-go-round and is tied to its centre. Merry-go-round is rotating about an axis passing through its centre.                                                                                                                                      [4M]

  1. What will be your observation when you are standing outside the merry-go- round? Explain it.
  2. What will be your observation when you are standing at the centre of the merry-go-round? Explain it.

Solution: The figure shows a ball tied at one end of a string, the other end of which is tied at the centre of the merry-go-round which is rotating. As the ball is left, the string becomes taut showing that it is under tension. A person standing at M on the ground outside the merry-go-round finds that the ball is moving on a circular path (shown by dotted lines), while a person standing on the merry-go-round at A finds that the ball is stationary, placed just in front of him at P. The difference in the observations of two persons at M and A can be explained as follows:

Explanation:
(i). For the person outside the merry-go-round, i.e. at M, the ball moves in a circular path because the tension in the string provides the centripetal force needed for circular motion.

(ii). But for the person at A, the following two forces act on the ball: (i) the tension in the string towards the centre of the merry-go-round and (ii) the centrifugal force away from the centre. The two forces are equal and opposite, so the net force on the ball is zero, and hence, it remains stationary.

 

Chapter 2: Work, Energy and Power

Q. 1. A force is applied on a body of mass 20 kg moving with a velocity of 40 ms-1. The body attains a velocity of 50 ms-1 in 2 seconds. Calculate the work done by the body.                                                                                                            [2M]

Solution: v = u + at 

begin mathsize 12px style straight F equals straight m fraction numerator open parentheses straight v minus straight u close parentheses over denominator straight t end fraction equals ma
Displacement equals fraction numerator straight v squared minus straight u squared over denominator 2 straight a end fraction
we space know space that
Work space equals space Force space cross times space Displacement
straight W equals ma cross times fraction numerator straight v squared minus straight u squared over denominator 2 straight a end fraction equals 1 half straight m open parentheses straight v squared minus straight u squared close parentheses
straight W equals 1 half cross times 20 cross times open parentheses 2500 minus 1600 close parentheses
straight W equals 1 half cross times 20 cross times 900 equals cross times 9000 straight J end style

Q. 2. How is work done by a force measured when the force:                                                                              [2M]

  1. is in the direction of displacement?
  2. is in an angle to the direction of displacement?
Solution: W = FS cosθ
If the force is in the direction of displacement
θ = 0°
W = FS
If the force is at angle to the direction of displacement
W = FScosθ
Here, F is the force and s is the displacement and θ is the direction in which force is applied.

Q. 3. An engine can pump 30,000 litres of water to a vertical height of 45 metre in 10 minutes. Calculate the work done by the machine and the power.
(Density of water = 103 kg/m3, 1000 litre = 1 m3, g = 9.8ms-2)                                                                    [3M]

Solution: Workdone = Potential energy

potential energy = mgh = 30000 × 9.8 × 45 = 13230000 Joule

=1323 kJ

begin mathsize 12px style Power equals Workdone over time
Power equals fraction numerator 13230 over denominator 10 cross times 60 end fraction equals 22.05 space kW end style


Q. 4. An object 'P' of mass m is lifted from a point A on ground to point B at a height 'h' above the Earth by Rina and Mita, but the path taken for doing it is different by both as shown                                                                                             [3M]

  1. Calculate the work done in both the situations.
  2. In the above given cases, which force is doing positive work and which one is doing negative work?
Solution: 
(i) Work done F × S
= ma × S
= m × g × h
= mgh (potential energy)
In both situations, W = mgh, since it is independent of the path followed and depends only on the initial and final positions.
 

(ii) Muscular force is doing positive work as it is in the direction of motion.
Gravitational force is doing negative work as it is opposite to the direction of motion.

Q. 5.                                                                                                                                                                     [4M]

(i)State the energy in the following while in use:

  1. Burning of a candle.
  2. A steam engine

(ii) On what basis would you classify an energy source as renewable? State two advantages and two limitations of the energy received from the Sun.

Solution: 
(i) (a)Burning of a candle: Chemical energy to light energy
(b)Steam engine: Chemical energy to heat energy to mechanical energy

(ii)Renewable energy resources are those which are present in our earth or atmosphere and which can be used an infinite number of times without getting exhausted.
Advantages:
1. It can be used in rural or remote areas.
2. Solar energy can be used for various purposes like for cooking and electricity.
Limitations:
1. Solar energy cannot be used in the night.
2. Efficiency of converting solar energy to another energy is very low.

Chapter 3: Machines

1. A type of single pulley is very often used as a machine even though it does not give any mechanical advantage.       [2M]

  1. Name the type of pulley used.
  2. For what purpose is such a pulley used?
Solution: 
  1. Single fixed pulley
  2. This type of pulley is used to change the direction of the force applied.

2. Draw a simplified diagram of a lemon crusher, indicting of load and effort.                                                              [2M]

Solution: 


3. A coolie is pushing a box weighing 1500 N up an inclined plane 7.5 m long on to a platform 2.5 m above the ground. [3M]

  1. Calculate the mechanical advantage of the inclined plane.
  2. Calculate the effort applied by the coolie.
Solution:
(i) Mechanical advantage of inclined plane = begin mathsize 12px style equals space fraction numerator length space of space inclined space plane over denominator Height end fraction end style
(ii) begin mathsize 12px style equals fraction numerator 7.5 mm over denominator 2.5 mm end fraction equals 3
Hence space effort space equals space fraction numerator 1500 straight N over denominator 3 end fraction equals space 500 straight N end style


4. Derive a relationship between the mechanical advantage, the velocity ratio and the efficiency of a machine.               [3M]

Solution:

begin mathsize 12px style Efficiency space straight eta space equals space fraction numerator Work space output over denominator work space input end fraction
straight eta space equals space fraction numerator straight L cross times straight d over denominator straight E cross times straight d subscript straight E end fraction equals straight L over straight E cross times straight d over straight d subscript straight E equals straight L over straight E cross times fraction numerator 1 over denominator begin display style bevelled straight d subscript straight E over straight d subscript 1 end style end fraction
straight M. straight A equals Load over Effort semicolon straight V. straight R equals straight d subscript straight E over straight d subscript 1
straight eta equals MA over VR end style

 

Q. 5. A block and tackle pulley system has a velocity ratio of 3.                                                                                       [4M]

  1. Draw a labelled diagram of this system. In your diagram, indicate clearly the points of application and the directions of the load and the effort.
  2. Why should the lower block of this pulley system be of negligible weight?
Solution: 
  1. (i) If w is the total weight of the pulleys in the lower block, then in the balanced position.

    begin mathsize 12px style Efficiency space equals space MA over VR equals fraction numerator straight n minus begin display style straight W over straight E end style over denominator straight n end fraction equals space 1 minus straight W over nE end style
  2. Efficiency gets reduced due to the weight of lower block pulleys. More the weight of the lower block pulleys, the less is the efficiency. Hence, for greater efficiency, the pulleys in the lower block should be as light as possible.

Chapter 4: Refraction of Light at Plane Surfaces 

Q. 1.                                                                                                                                                                           [2M]

  1. The refractive index of glass with respect to air is 1.5. What is the value of refractive index of air with respect to glass?
  2. A ray of light is incident as a normal ray on the surface of separation of two different mediums. What is the value of the angle of incidence in this case?
Solution: 
  1.  begin mathsize 12px style straight mu presubscript straight g subscript straight a equals fraction numerator 1 over denominator straight mu presubscript straight a subscript straight g end fraction equals fraction numerator 1 over denominator 1.5 end fraction equals 0.667 end style
  2. Angle of incidence is Zero.

Q. 2. What are the necessary conditions for the total internal reflection?                                                                         [2M]

Solution: Two necessary conditions for total internal reflection:

  1. The light must travel from a denser to a rarer medium.
  2. The angle of incidence must be greater than the critical angle for the pair of media.

 Q. 3.                                                                                                                                                                         [2M]

  1. Can the absolute refractive index of a medium be less than one?
  2. A coin placed at the bottom of a beaker appears to be raised by 4.0 cm. If the refractive index of water is 4/3, find the depth of the water in the beaker.
Solution: 
  1. No
  2. Real depth=?
    begin mathsize 12px style Apparent space depth equals fraction numerator Real space depth over denominator refractive space index end fraction
shift space equals space real space depth space minus space apparent space depth
Shift space equals space Real space depth open square brackets 1 minus 1 over straight mu close square brackets
4 equals Real space depth open parentheses 1 minus fraction numerator 1 over denominator 4 divided by 3 end fraction close parentheses space 4 equals Real space depth open parentheses 1 minus 3 over 4 close parentheses space 4 space equals space Real space depth open parentheses 1 fourth close parentheses
Real space depth space equals space 16 space cm end style

Q. 4. The refractive index of glass is 1.5. From a point P inside a glass block, draw rays PA, PB and PC incident on that glass-air surface at an angle of 30o, 42o and 60o respectively.                                                                                                             [3M]

  1. In the diagram show the approximate direction of these rays as they emerge out of the block.
  2. What is the angle of refraction for the ray PB?
Solution:
  1. (a) μ = 1.5
    begin mathsize 12px style Sin space straight i subscript straight c equals 1 over straight mu equals fraction numerator 1 over denominator 1.5 end fraction equals 0.667 end subscript
straight i subscript straight c equals 42 degree end subscript end style
  2. As angle of incidence the glass block is 42°

    begin mathsize 12px style Sinr over Sini equals straight mu presubscript straight a subscript straight g cross times Sin space 42 degree
sin space 42 degree equals 2 over 3 and space straight mu presubscript straight a subscript straight g equals 3 over 2
Sinr equals 3 over 2 cross times 2 over 3 equals 1
straight r equals 90 degree end style

    This also follows from the fact that the ray PB is incident at the critical angle.

Q. 5.  A ray of light of wavelength 5400Å suffers refraction from air to glass. Taking aμg = 1.5 , find the wavelength of light in glass. 3M]

Solution: Refractive index of glass wrt air

begin mathsize 12px style straight mu presubscript straight a subscript straight g equals 1.5
straight mu presubscript straight a subscript straight g equals fraction numerator wavelength space of space light space in space air over denominator wavelength space of space light space in space glass end fraction
1.5 equals fraction numerator wavelength space of space light space in space air over denominator wavelength space of space light space in space glass end fraction
1.5 equals fraction numerator 5400 straight Å over denominator wavelength space of space light space in space glass end fraction
wavelength space of space light space in space glass space equals space 2 over 3 cross times 5400 straight Å equals 3600 straight Å end style

Chapter 5: Refraction through a Lens


Q. 1. Riya claims to have obtained an image twice the size of the object with a concave lens. Is she correct? Give a reason for your answer.                                                                                                                                                                   [2M]

Solution: False. A concave lens always gives a diminished, virtual image irrespective of the position of the object from the lens.

Q. 2. A lens forms the image of an object placed at a distance 15 cm from it, at a distance 60 cm in front of it. Find: (i) the focal length, (ii) the magnification, and the nature of image.                                                                                                [2M]

Solution: Object distance, u = -15 cm

Image distance, v = -60 cm

  1. Lens Formula is
    begin mathsize 12px style 1 over straight v minus 1 over straight u equals 1 over straight f rightwards double arrow fraction numerator 1 over denominator negative 60 end fraction minus fraction numerator 1 over denominator negative 15 end fraction equals 1 over straight f
1 over straight f equals 1 over 15 minus 1 over 60 equals 3 over 60 rightwards double arrow straight f equals 20 cm end style

  2. For a lens, magnification is 
    begin mathsize 12px style straight m equals straight v over straight u rightwards double arrow straight m equals fraction numerator negative 60 over denominator negative 15 end fraction rightwards double arrow straight m equals plus 4 end style
    Image is erect, virtual and magnified.

Q. 3. A linear object is placed on the axis of a lens. An image is formed by refraction in the lens. For all positions of the object on the axis of the lens, the position of the image is always between the lens and the object.                                                    [3M]

  1. Name the lens.
  2. Draw a ray diagram to show the formation of the image of an object placed in front of the lens at any position of your choice except infinity.
Solution:
  1. Concave lens

 

Q. 4. An object AB is placed between 2F1 and F1 on the principal axis of the convex lens as shown in the diagram below:   [4M]



Copy the diagram and using the rays starting from point A, obtain the image of the object formed by the lens.

Solution:

Chapter 6: Spectrum

Q. 1.                                                                                                                                                                     [2M]

  1. Name a prism required for obtaining a spectrum of Ultraviolet light.
  2. Name the radiations which can be detected by a thermopile.
Solution: 
  1. Quartz prism
  2. Heat radiation

Q. 2. Name the radiations:                                                                                                                                      [3M]

  1. That are used for photography at night.
  2. That are used for detection of fracture in bones.
  3. Whose wavelength ranges from 100 Å to 4000 Å (or 10 nm to 400nm).
Solution: 
  1. Infrared rays
  2. X-rays
  3. Ultraviolet radiation

Q. 3. A type of electromagnetic wave has wavelength50Å                                                                                          [3M]

  1. Name the wave.
  2. What is the speed of the wave in vacuum?
  3. State one use of this type of wave.
Solution:
  1. X-ray
  2. Speed of EM wave in vacuum is
  3. They are used for detection of a fracture in bones.

Q. 4. A ray of white light is passed through a glass prism and spectrum is obtained on a screen.                                   [3M]

  1. Name the seven colours of the spectrum in order.
  2. Do the colours have the same width in the spectrum?
  3. Which of the colour of the spectrum of white light deviates (i) the most? (ii) the least? 
Solution: 
  1. Violet, Indigo, Blue, Green, Yellow, Orange, Red.
  2. No, different colours have different widths in the spectrum.
  3. (i) Violet colour is deviated the most. (ii) Red colour is deviated the least

Q. 5. The diagram shown below shows the path taken by a narrow beam of yellow monochromatic light passing through an equiangular glass prism. Now the yellow light is replaced by a narrow beam of white light incident at the same angle. Draw another diagram to show the passage of the beam through the prism and label it to show the effect of prism on the white light.  [3M]

Solution:

 


 


 

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