Physics with Tanveer kurd Behramshahi Mastung.
5000 Words
Skip to content
Physics10
According to Syllabus (Test Your Skill)
TOGGLE NAVIGATION
Chapter 12 Long Questions
Q. 12.1. What do you understand by reflection of light? Draw a diagram to illustrate reflection at a plane surface.
Q. 12.2. Describe the following terms used in reflection:
(i) normal (ii) angle of incidence (iii) angle of reflection
Q.12.3. State laws of reflection. Describe how they can be verified graphically.
Q. 12.4. Define refraction of light. Describe the passage of light through parallel-sided transparent material.
Q.12.5. Define the following terms used in refraction:
(i) angle of incidence (ii) angle of refraction
Q.12.6. What is meant by refractive index of a material? How would you determine the refractive index of a rectangular glass slab?
Q.12.7. State the laws of refraction of light and show how they may be verified using rectangular glass slab and pins.
Q.12.8. What is meant by the term total internal reflection?
Q.12.9. State the conditions for total internal reflection.
Q.12.10. What is critical angle? Derive a relationship between the critical angle and the refractive index of a substance.
Q.12.11. What are optical fibers? Describe how total internal reflection is used in light propagating through optical fibers.
Q.12.12. Define the following terms applied to a lens:
(i) principal axis (ii) optical center (iii) focal length
Q.12.13. What is meant by the principal focus of a (a) convex lens (b) concave lens? Illustrate your answer with ray diagrams.
Q.12.14. Describe how light is refracted through convex lens.
Q.12.15. With the help of a ray diagram, how you can show the use of thin converging lens as a magnifying glass.
Q.12.16. A coin is placed at a focal point of a converging lens. Is an image formed? What is its nature?
Q.12.17. What are the differences between real and virtual images?
Q.12.18. How does a converging lens form a virtual image of a real object? How does a diverging lens can form a real image of a real object?
Q.12.19. Define power of a lens and its units.
Q.12.20. Describe the passage of light through a glass prism and measure the angle of deviation.
Q.12.21. Define the terms resolving power and magnifying power.
Q.12.22. Draw the ray diagrams of (i) simple microscope (ii) compound microscope (iii) refracting telescope
Q.12.23. Mention the magnifying powers of the following optical instruments:
(i) simple microscope (ii) compound microscope (iii) refracting telescope
Q.12.24. Draw ray diagrams to show the formation of images in the normal human eye.
Q.12.25. What is meant by the terms nearsightedness and farsightedness? How can these defects be corrected?
CONCEPTUAL QUESTIONS
Q.12.1 A man raises his left hand in a plane mirror, the image facing ‘him is raising his right hand. Explain why.
Q.12.2 In your own words, explain why light waves are refracted at a boundary between two materials.
Q.12.3 Explain why a fish under water appears to be at a different depth below the surface than it actually is. Does it appear deeper or shallower?
Q.12.4 Why or why not concave mirrors are suitable for makeup?
Q.12.5. Why is the driver’s side mirror in many cars convex rather than plane or concave?
Q.12.6. When an optician’s testing room is small, he uses a mirror to help him test the eyesight of his patients. Explain why.
Q.12.7. How does the thickness of a lens affect its focal length?
Q.12.8. Under what conditions will a converging lens form a virtual image?
Q.12.9. Under what conditions will a converging lens form a real image that is the same size as the object?
Q.12.10. Why do we use refracting telescope with large objective lens of large focal length?
Q. 12.1. What do you understand by reflection of light? Draw a diagram to illustrate reflection at a plane surface.
Answer: When light ray is completely returns- back into some medium after felling
from a polished surface is called “reflection of light”
Draw:
Q. 12.2. Describe the following terms used in reflection:
(i) normal (ii) angle of incidence (iii) angle of reflection
Answer:
Normal:
‘The perpendicular drawn on the reflecting plane, at point of incidence of ray of light as called “normal”.
Angle of Incidence
The angle between incident ray and normal is called angle of incidence.
Angle of reflection
The angle between reflected ray and normal is called angle of reflection.
Q.12.3. State laws of reflection. Describe how they can be verified graphically.
Answer: There are two laws of reflection of light.
a. The incident ray the normal and the reflected ray at the point of incidence all lie in the same plane.
b. The angle of incidence is equal to the angle of reflection.
Q. 12.4. Define refraction of light. Describe the passage of light through parallel-sided transparent material.
Answer: In physics, refraction is the change in direction of a wave passing from one medium to another or from a gradual change in the medium. Refraction of light is the most commonly observed phenomenon, but other waves such as sound waves and water waves also experience refraction.
If a ray of light hits the surface of a sheet of glass, some light will be reflected by the surface of the glass. However, much of the light will pass through the glass, because glass is transparent. This bending of a ray of light when it passes from one substance into another substance is called refraction.
Q.12.5. Define the following terms used in refraction:
(i) angle of incidence (ii) angle of refraction
Answer:
(i) angle of incidence
The angle shown in the figure between incident ray (AO) and the normal (ON) is called angle of incident which is denoted by <AON = < θ1
(ii) angle of refraction
The angle between the reflected ray (OB) and the normal (ON) is called angle of reflection and is denoted by <ONB = < θ2
Q.12.6. What is meant by refractive index of a material? How would you determine the refractive index of a rectangular glass slab?
Answer: The ratio of sine of angle of incidence to the angle of refraction is called refractive index the refractive index of a glass slab is determined experimentally by using formula.
Refractive index = sin θ1 / sin θ2
Q.12.7. State the laws of refraction of light and show how they may be verified using rectangular glass slab and pins.
Answer:
1st Law .
It states that incident ray, normal and refracted ray lie in same plane.
2nd Law
It states that ratio of sine of angle of incidence to the sine of angle of refraction is constant (Snell’s law) .
Q.12.8. What is meant by the term total internal reflection?
Answer: When a light ray is incident upon the separating surface, coming from denser medium for which angle of reflection in rare medium is greater than 90° , then its is called total internal reflection.
Q.12.9. State the conditions for total internal reflection.
Answer: The following are conditions of total internal reflection.
(i) The incident ray should come from denser medium at angle of incidence greater then critical angle.
(ii) The totally reflected ray is received in the same denser medium.
Q.12.10. What is critical angle? Derive a relationship between the critical angle and the refractive index of a substance.
Answer: Critical angle
The critical angle is defined as the angle of incidence that provides an angle of refraction of 90-degrees. Make particular note that the critical angle is an angle of incidence value. For the water-air boundary, the critical angle is 48.6-degrees.
Relation Between Critical Angle And Refractive Index. In Optics, The angle of incidence to which the angle of refraction is 900 is called critical angle. The ratio of velocities of a light ray in the air to the given medium is refractive index.
Q.12.11. What are optical fibers? Describe how total internal reflection is used in light propagating through optical fibers.
Answer: Optical fibers: It is a hair size thread made up of glass for plastic through which light can be traveled.
a. The inner part of fiber optic is called core that carries light.
b. The outer part is concentric shell caused cladding.
Total internal reflection used in fiber optics
When light traveling in an optically dense medium hits a boundary at a steep angle (larger than the critical angle for the boundary), the light is completely reflected. This is called total internal reflection. This effect is used in optical fibers to confine light in the core.
Q.12.12. Define the following terms applied to a lens:
(i) principal axis (ii) optical center (iii) focal length
Answer:
(i) Principal axis
The line passing through pole and focal point is called principle axis of lone.
(ii) Optical center
The central symmetric point of a lens is called optical center.
(iii) Focal length
The distance between focal point and optical center of lens is called its focal length.
Q.12.13. What is meant by the principal focus of a (a) convex lens (b) concave lens? Illustrate your answer with ray diagrams.
Answer:
(a) Convex lens: The principal focus of a convex lens is defined as the point on which the principal axis of the light is parallel to the principal axis that converges after the refraction from the lens.
b) Concave lens: The principal focus of concave lens is when the light rays get diverged and appear to form a single point.
Ray Diagrams:
Q.12.14. Describe how light is refracted through convex lens.
Answer: A convex lens is a system of two prisms placed base to base as shown in Convex lens bends the light towards the principal axis that is towards thickest pan of the lens after refraction. Rays of light that pass through the lens are brought closer together (they converge). A convex lens is a converging lens. When parallel rays of light pass through a convex lens the refracted rays converge at one point called the principal focus.
Q.12.15. With the help of a ray diagram, how you can show the use of thin converging lens as a magnifying glass.
Answer: A magnifying glass is a convex lens used to make an object appear much larger than it actually is. This works when the object is placed at a distance less than the focal length from the lens. The image is:
upright (the right way up)
magnified (larger than the object)
virtual (cannot be produced on a screen)
Ray diagram for an object placed less than one focal length from a convex lens
Only the person using the magnifying glass can see the image. The image cannot be projected onto a screen because it is a virtual image.
Q.12.16 A coin is placed at a focal point of a converging lens. Is an image formed? What is its nature?
Answer: If a coin (object) is placed at a focal point of a converging lens its image is not formed because rays become parallel after passing through the lens.
Q.12.17. What are the differences between real and virtual images?
Answer: Real image is that image which can be formed on a screen but the virtual image can’t’formed on a screen.
Real images are formed when light rays after reflection or refraction converge at a point before a mirror or lens. While virtual images are formed when the light rays diverge after reflection or refraction.
Real images appear on the screen as against virtual images never appear on the screen.
Converging types of lenses are used to produce a real image. Whereas diverging lens is used for the formation of virtual images.
Real images are inverted in nature. While virtual images appear erect.
Generally, concave mirrors or convex lenses form real images. Plane mirror, convex mirror, and concave lens are regarded as the virtual image forming surfaces.
The front region of the mirror forms real images. Whereas virtual images are assumed to be formed behind the mirror.
Real images are formed due to the actual interaction of real rays. However, virtual images are formed when light rays imaginary interact with each other.
In the case of the real image, the light rays diverge from the same side of the mirror after converging and forming the real image. While in the case of the virtual image, the light rays assumed to diverge from a point somewhere behind the mirror.
Q.12.18. How does a converging lens form a virtual image of a real object? How does a diverging lens can form a real image of a real object?
Answer: In case of converging lens: A virtual image is formed of a real object when it is placed between the focal point and optical center of the lens.
As shown above, real images are produced when the object is located a distance greater than one focal length from the lens. A virtual image is formed if the object is located less than one focal length from the converging lens. To see why this is so, a ray diagram can be used.
Q.12.19. Define power of a lens and its units.
Answer: Power of a lens is defined as the inverse of focal length (in meters) of the lens. It is a measure of the amount of deviation of light ray produced by a lens, more the power, more is the deviation. Unit of power is Dioptre (D).
P= 1/ƒ
Convex lens has positive power and concave lens has negative power. Power of a plane glass plate is 0. Power of combinations of lenses kept close to each other is equal to the sum of individual powers of each lens.
Q.12.20. Describe the passage of light through a glass prism and measure the angle of deviation.
Answer: The incident ray bends towards the normal when it enters the prism and while leaving the prism it bends away from the normal. With the increase in the angle of incidence, the angle of deviation decreases. After attaining the minimum value, it increases with an increase in the angle of incidence.
Precautions
For drawing the boundary of the prism, a sharp pencil should be used.
Soft board and pointed pins should be used.
The distance between the pins should be 5cm or more.
The pins should be fixed vertically and should be encircled when they are removed from the board.
The angle of incidence should be between 30° and 60°.
The arrows drawn for incident ray, reflected ray and emergent ray should be proper.
For viewing the col-linearity of all the four pins and images, the head should be slightly titled on either side. While doing this it can appear as all are moving together.
Q.12.21. Define the terms resolving power and magnifying power.
Answer: Magnification
Magnification is the ability to make small objects seem larger, such as making a microscopic organism visible. Magnification is the process of enlarging something only in appearance, not in physical size. This enlargement is quantified by a calculated number also called “magnification. ”
Resolution: Resolution is the ability to distinguish two objects from each other.
Q.12.22. Draw the ray diagrams of (i) simple microscope (ii) compound microscope (iii) refracting telescope
Answer: (i) Simple Microscope
A simple microscope is used to obtain small magnifications. It is usually used for study of microscopic algae, fungi and biological specimen.
(ii) Compound Microscope
(iii) Refracting Telescope
Q.12.23. Mention the magnifying powers of the following optical instruments:
(i) simple microscope (ii) compound microscope (iii) refracting telescope
Answer: (i) Simple Microscope
The magnifying power of a simple microscope is given by:
M = 1 + d / ƒ
where ƒ is the focal length of lens and d is near point of eye.
(ii) Compound Microscope
The magnification of the compound microscope is given by:
where L is the length of a compound microscope which is equal to the distance between objective and eye piece, d is distance of final image from eye, f0 and fe are the focal lengths of objective and eye piece respectively.
(iii) Refracting Telescope
Magnifying power of a telescope is defined as the ratio of the angle subtended at the eye by the image formed at the least distance of distinct vision to the angle subtended at the eye by the object lying in infinity.
Where f0= focal length of the object fe= focal length of the eye piece ; D= least distance of the distinct vision.
Q.12.24. Draw ray diagrams to show the formation of images in the normal human eye.
Answer: A ray-diagram can be used to show how light passes from a point on a real object (located somewhere in space outside the body) to the corresponding position on the image of the object on the retina at the back of the eye. The following example is explained below:
Q.12.25. What is meant by the terms nearsightedness and farsightedness? How can these defects be corrected?
Answer: Nearsightedness: Nearsightedness, or myopia, is the inability to see distant objects and is corrected with a diverging lens to reduce power.
Farsightedness: Farsightedness, or hyperopia, is the inability to see close objects and is corrected with a converging lens to increase power.
Both nearsightedness and farsightedness can be treated with corrective eyeglasses and contact lenses. The lenses work by changing the way light rays bend into the eyes.
Q.12.1 A man raises his left hand in a plane mirror, the image facing ‘him is raising his right hand. Explain why.
Answer: Laterally laterally inverted image is formed in case of a plane mirror. So if the object (person) raises his left hand then its image will raise his right hand and vice versa.
Q.12.2 In your own words, explain why light waves are refracted at a boundary between two materials.
Answer: It is one or the basic properties of light waves. Light waves refract at the boundary of two media having different values of refractive index.
Q.12.3 Explain why a fish under water appears to be at a different depth below the surface than it actually is. Does it appear deeper or shallower?
Answer: When we see fish under water the light rays travelling from water to air, coming out rays bend from their straight path due to effect of refraction it seems at less depth than it actually is. So it appear shallower as showing in figure.
Q.12.4 Why or why not concave mirrors are suitable for makeup?
Answer: When face is placed between the concave mirror and its focus, it produces a magnified image. This enlarged image of face is helpful in makeup as even pores of skin are clearly visible.
Q.12.5. Why is the driver’s side mirror in many cars convex rather than plane or concave?
Answer: Convex mirror is used as side mirror in cars because it produces image that are smaller than the size of the objects. This increases the view for the driver.
Q.12.6. When an optician’s testing room is small, he uses a mirror to help him test the eyesight of his patients. Explain why.
Answer: When optician uses a mirror to test the eye sight of his parents. He places a mirror in the half distance of the required because he knows the image is formed behind the mirror at the same as the object is placed in front of the mirror.
Q.12.7. How does the thickness of a lens affect its focal length?
Answer: A lens with more “bending power” has a shorter focal length, because it alters the path of the light rays more effectively than a weaker lens. But for thicker lenses, how thick they are does make a difference, and in general, results in a shorter focal length.
Q.12.8. Under what conditions will a converging lens form a virtual image?
Answer: A virtual image is formed if the object is located less than one focal length from the converging lens. To see why this is so, a ray diagram can be used.
A ray diagram for the case in which the object is located in front of the focal point is shown in the diagram at the right.
Q.12.9. Under what conditions will a converging lens form a real image that is the same size as the object?
Answer: When an object is place at 2F then its image formed at 2F on the other side of the lens having same size. It is real, inverted and same size image as object.
Physics10
According to Syllabus (Test Your Skill)
TOGGLE NAVIGATION
Chapter 11 Sound Long Questions
Q.1 What is the necessary condition for the production of sound?
Q.2 What is the effect of the medium on the speed of sound? In which medium sound travels more faster: air, solid or liquid? Justify your answer.
Q. 3 How can you prove the mechanical nature of sound by a simple experiment?
Q.4 What do you understand by the longitudinal wave? Describe the longitudinal nature of sound waves.
Q. 5 Sound is a form of wave. List at least three reasons to support the idea that sound is a wave.
Q. 6 We know that waves manifest phenomenon of reflection, refraction and diffraction. Does sound also manifest these characteristics?
Q.7 What is the difference between the loudness and intensity of sound? Derive the relationship between the two.
Q.8 On what factors does the loudness of sound depend?
Q.9 What do you mean by the term intensity level of the sound? Name and define the unit of intensity level of sound.
Q.10 What are the units of loudness? Why do we use logarithmic scale to describe the range of the sound intensities we hear?
Q.11 What is difference between frequency and pitch? Describe their relationship graphically.
Q.12 Describe the effect of change in amplitude on loudness and the effect of change in frequency on pitch of sound.
Q.13 If the pitch of sound is increased, what are the changes in the following?
a. the frequency b. the wavelength c. the wave velocity d. the amplitude of the wave
Q.14 If we clap or speak in front of a building while standing at a particular distance, we rehear our sound after sometime. Can you explain how does this happen?
Q. 15 What is the audible frequency range for human ear? Does this range vary with the age of people? Explain.
Q.16 Explain that noise is a nuisance.
Q.17 Describe the importance of acoustic protection.
Q.18 What are the uses of ultrasound in medicine?
Q.1 What is the necessary condition for the production of sound?
Answer: Sound wave can be produced by vibrating a body and travel in a medium whose particles can vibrate. The frequency of vibrations must be greater than 20Hz and Jess than 20,000Hz. In solids the sound waves have faster speed than in air or liquid due to larger elasticity.
Q.2 What is the effect of the medium on the speed of sound? In which medium sound travels more faster: air, solid or liquid? Justify your answer.
Answer: Sound waves arc mechanical waves so medium has effect on the speed of sound waves. In solids the sound waves have faster speed than in air or Liquid due to larger elasticity.
Q. 3 How can you prove the mechanical nature of sound by a simple experiment?
Answer: The sound waves are “mechanical waves”. It require material medium. It can be proved by placing an electric bell inside a glass jar where vacuum is produced. The working electric bell is made ON, but sound produced by it cannot be heard, due to vacuum and no material medium be present around it. While before producing vacuum sound will he heard.
Q.4 What do you understand by the longitudinal wave? Describe the longitudinal nature of sound waves.
Answer:
Longitudinal Waves: The waves are said to be longitudinal if the particles of the medium vibrate in the same direction as the direction of propagation of waves. Sound waves are mechanical and longitudinal in nature. It means the particles of the medium (air, liquid or solid) vibrate in the same direction as the direction of the sound waves travel.
Q. 5 Sound is a form of wave. List at least three reasons to support the idea that sound is a wave.
Answer:
Sound is a form of wave.
It gives the sensation of hearing. If we listening sound the membrane of our ear starts vibrating.
Ultra-sounds (high energy waves) are used in medical sciences.
Q. 6 We know that waves manifest phenomenon of reflection, refraction and diffraction. Does sound also manifest these characteristics?
Answer: Yes, sound waves also exhibit the characteristics like reflection, diffraction and refraction.
Echo is the practical example for the reflection of sound waves.
Listening of the person in other room is an example of diffraction of sound waves.
There are example to show the refraction of sound waves by which their speed and direction is change.
Q.7 What is the difference between the loudness and intensity of sound? Derive the relationship between the two.
Answer:
Loudness: The magnitude of “auditory sensation” due to sound waves is called loudness. Faint and loud voice can be distinguished by the magnitude of loudness.
Intensity of sound: The energy transferred by sound waves per unit area per second. When unit area in at 900 to direction of propagation of sound waves, is called intensity of sound. Its unit are “watt per square meter”.
Relation between loudness and Intensity:
The audible sound waves for a normal human ear have intensity ranging from 10-12 Wm-2 to 1Wm-2. it is a very large range; therefore it is scaled in powers of ten.
Power of ten:
The lowest intensity to which ear can response is 10-12 Wm-2. It is taken as reference value and is written as zero bel. Therefore on bel intensity is 10-11 Wm-2 or it is equal 10db (decibel).
Experimentally it is confirmed that loudness is directly proportional to logarithm of intensity value we can write as
L ∝ log I
L = (constant) log I
L = k log I
Here k is constant of proportionality which is called proportionality constant.
Q.8 On what factors does the loudness of sound depend?
Answer:
Loudness: Loudness is the characteristic of sound by which loud and faint sounds can be distinguished.
Factors on which loudness depends upon:
a. Amplitude of vibrating body.
b. Area of vibrating body.
c. Distance from vibrating body.
d. Physical condition of ear.
Q.9 What do you mean by the term intensity level of the sound? Name and define the unit of intensity level of sound.
Answer:
Intensity of Sound: Sound energy passing per second through a unit area held perpendicular to the direction of propagation or sound waves is called intensity of sound.
Unit: Its unit is watt per square metre (Wm-2)
Q.10 What are the units of loudness? Why do we use logarithmic scale to describe the range of the sound intensities we hear?
Answer:
Unit of loudness: Decibel is the unit of loudness (dB)
Why do we use logarithmic scale to describe the range of the sound intensities we hear?
It’s because the ear responds to sound intensity logarithmically. And in turn that’s because nature produces sound intensities over an extremely wide range – if our ears could not cope with that range, there would be little purpose in having ears.
Q.11 What is difference between frequency and pitch? Describe their relationship graphically.
Answer: The number of wave lengths passing through a point in one second is called frequency. Its units are hertz (HZ) and, the pitch is quality of sound due to which a shrill and grave voice can be distinguished. The greater is frequency of sound, the larger is pitch of sound and vice-versa.
Q.12 Describe the effect of change in amplitude on loudness and the effect of change in frequency on pitch of sound.
Answer: The effect of change of amplitude of sound waves the energy changes and due to which loudness may also change.
The magnitude of sensation of sound is called “loudness”. When frequency of sound wave effect the pitch of sound waves. The greater is frequency, the larger is it pitch and vise-versa.
Q.13 If the pitch of sound is increased, what are the changes in the following?
a. the frequency b. the wavelength
c. the wave velocity d. the amplitude of the wave
Answer: Its frequency will be increased.
Q.14 If we clap or speak in front of a building while standing at a particular distance, we rehear our sound after sometime. Can you explain how does this happen?
Answer: It is due. to the reflection of sound waves. After incident on the walls of they come back into the same medium. That is why we rehear the sound after some time. It is called echo.
Q. 15 What is the audible frequency range for human ear? Does this range vary with the age of people? Explain.
Answer: Sound in the form of continuous note, have audible frequency range from 20Hz to 20,000Hz. This means that a normal human ear cannot hear sound wave having frequencies less than 20Hz and grater than 20,000Hz . This range of audible frequency is different fro ears of different persons. Also the width of this range of audible frequencies decreases with age. Young children can hear sound of 20,000Hz, but old people cannot hear sound even above 15000Hz.
Q.16 Explain that noise is a nuisance.
Answer: A noise nuisance is a noteworthy and unreasonable amount of sound from a neighboring premises. The nuisance could be coming from a domestic or commercial property and affects you and your life in a significant way which is more than a simple annoyance.
The main factors that officers and the courts will take into account are:
time of day
location
duration of each individual noise event
volume of the noise
character of the noise
frequency with which noisy events occur
It is not necessary for officers to take noise readings to establish if a nuisance exists, although sometimes this can help. On the whole the judgement of experienced
- Writer
