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Q1. In the following questions, a statement of Assertion is given by the corresponding statement of Reason. Of the statements, mark the correct answer as:
- If both Assertion and Reason are true and Reason is the correct explanation of Assertion.
- If both Assertion and Reason are true, but Reason is not the correct explanation of Assertion.
- If Assertion is true, but Reason is false.
- If Assertion is false, but Reason is true.
- If both Assertion and Reason are false. Assertion: The speed of light in a rarer medium is greater than that in a denser medium. Reason: One light year equal to 9.5 × 10 km.
1 Mark
Q2. In the following questions, a statement of Assertion is given by the corresponding statement of Reason. Of the statements, mark the correct answer as:
- If both Assertion and Reason are true and Reason is the correct explanation of Assertion.
- If both Assertion and Reason are true, but Reason is not the correct explanation of Assertion.
- If Assertion is true, but Reason is false.
- If Assertion is false, but Reason is true.
- If both Assertion and Reason are false. Assertion: ENT specialist use a concave mirror as a head mirror to concentrate light on the body parts like eye, ear, nose etc. Reason: A concave mirror is more effective and easily available.
1 Mark
Q3. In the following questions, a statement of Assertion is given by the corresponding statement of Reason. Of the statements, mark the correct answer as:
- If both Assertion and Reason are true and Reason is the correct explanation of Assertion.
- If both Assertion and Reason are true, but Reason is not the correct explanation of Assertion.
- If Assertion is true, but Reason is false.
- If Assertion is false, but Reason is true.
- If both Assertion and Reason are false. Assertion: Keeping a point object fixed, if a plane mirror is moved, the image will also move. Reason: In case of a plane mirror, distance of object and its image is equal from any point on the mirror.
1 Mark
Q4. A student has obtained an image of a distant object on a screen to determine the focal length F of the given lens. His teacher after checking the image, gave him another lens of focal length F and asked to focus the same object on the same screen. The student found that to obtain a sharp image he has to move the lens away from the screen. From this finding we may conclude that both the lenses given to the student were:
- Concave and
- Convex and
- Convex and
1 Mark
AARPAN INSTITUTE
BHANDARA
Test / Exam Name: Light, Reflection & Refraction
Standard: 10th Subject: Science
Student Name: Section: Roll No.:
Questions: 22 Time: 01 00 hh:mm Marks: 50
SECTION-- A. MULTIPLE CHOICE QUESTION
Instructions
- ATTEMPT ALL THE QUESTION
- ATTEMPT ALL THE QUESTION
13
1 2
F 1 < F 2
F 1 < F 2
F 1 > F 2
- Concave and Q5. Study the following diagram and select the correct statement about the device 'X':
- Device 'X' is a concave mirror of radius of curvature 12cm.
- Device 'X' is a concave mirror of focal length 6cm.
- Device 'X' is a concave mirror of focal length 12cm.
- Device 'X' is a convex mirror of focal length 12cm.
1 Mark
Q6. A student obtains a sharp image of the distant window (W) of the school laboratory on the screen (S) using the given concave mirror (M) to determine its focal length. Which of the following distances should he measure to get the focal length of the mirror?
1. MW.
2. MS.
3. SW.
4. MW – MS.
1 Mark
Q7. A student is using a convex lens of focal length 10 cm to study the image formation by a convex lens for the various positions of the object. In one of his observations, he may observe that when the object is placed at a distance of 20 cm from the lens, its image is formed at (select the correct option):
- 20cm on the other side of the lens and is of the same size, real and erect.
- 40cm on the other side of the lens and is magnified, real and inverted.
- 20cm on the other side of the lens and is of the same size, real and inverted.
- 20cm on the other side of the lens and is of the same size, virtual and erect.
1 Mark
Q8. Beams of light are incident through the holes A and B and emerge out of box through the holes C and D respectively as shown in the Figure. Which of the following could be inside the box?
- A rectangular glass slab.
- A convex lens.
- A concave lens.
- A prism.
1 Mark
Q9. A convex mirror of focal length f forms an image of the size of the object. The
distance of the object from the mirror is:
1 Mark
Q10. A perfecting reflecting mirror has an area of 1cm. Light energy is allowed to fall on it for an hour at the rate of 10cm. The force that acts on the mirror is:
- N 3.35×
- N 6.7×
- N 3.35×
- 6.7×10 N
1 Mark
Q11. The boy walks towards the mirror at a speed of 1m/ s. At what speed does his image approach him?
2 Marks
Q12. List four precautions which a student should observe while determining the focal length of a given convex lens by obtaining image of a distant object on a screen.
2 Marks
SECTION- B. VERY SHORT ANSWER QUESTION
F 1 > F 2
1 nth n+1n f (n + 1)f (n − 1)f n - 1n f 2
- The formula to calculate the refractive index is:
- OR
Q20.
The bending of light as it passed from one transparent medium into another is called refraction. Place a pencil in an inclined position in a glass trough and fill three fourth of the trough with water.
- State true or false: The position of the portion of the pencil under water has changed.
- True
- False
- What shall be the reason for the change in the position of the pencil under water?
- Due to reflection
- Due to refraction
- Does the ray of light coming after reflection from the pencil undergo a deviation?
- Yes
- No
- What is the reason for the ray of light coming after reflection from the pencil undergo deviation?
- When light travels from air to air it deviates.
- When light travels from water to air it deviates.
- When light travels from water to oil it deviates.
- None of these
- Is there any change likely to occur if kerosene is used instead of water?
- Pencil appears to be bent less.
- Pencil does not bent.
- Pencil appears to be bent more.
- None of these Q21.
Sunil wants to see the micro organisms present in soil. He knows that he needs a microscope to see those tiny things. A microscope is an instrument used to see a small object to look bigger which helps us in a study of many tiny little species. Well, refraction also plays a huge role in the microscope.
- What kind of lens is used in microscope?
- Concave lens
- Convex lens
- Bifocal lens
- Plane lens
- The image formed by a convex lens can be.
- Virtual and magnified
4 Marks
n = cv n = vc n = cv v = nc
- Virtual and diminished
- Virtual and of same size
- Virtual image is not formed
- Absolute refractive index of any medium is always ______.
- Less than 1
- Greater than 1
- 1
- 0
- Power of convex lens is ______.
- Positive
- Positive
- The refracting surfaces obeys the ______.
- Law of reflection
- Law of refraction Q22.
Abin wanted to see the stars of the night sky. He knows that he needs a telescope to see those distant stars. There are two types of telescopes, reflecting telescopes which are made of mirrors and refracting telescope which are made of lenses. So he decided to take a refracting telescope. There are two lenses, the larger lense gathers and bends the light, while the smaller lens magnifies the image.
- What kind of lenses are used in the refracting telescope?
- Concave lens
- Convex lens
- Bifocal lens
- Both (a) and (b)
- The unit of power of lens is:
- Meter
- Centimeter
- Diopter
- M
- Objective lens will create a ______ image of the object being studied.
- Real
- Virtual
- Eyepiece lens takes the image created by objective lens and ______ it for your viewing.
- Diminishes
- Magnifies
- The lens of a telescope uses a ______ to make things look closer they really are.
- Reflection of light
- Refraction of light
4 Marks
- If both Assertion and Reason are false. Assertion: Keeping a point object fixed, if a plane mirror is moved, the image will also move. Reason: In case of a plane mirror, distance of object and its image is equal from any point on the mirror. Ans: 4. If Assertion is false, but Reason is true. Explanation: In case the mirror is moving parallel to its plane then velocity of the image wrt to the plane will be 0. ... The Velocity of the image is, 2 × Velocity of the mirror + c, that is equal to c, therefore, does not matter whether the mirror was moving or not, speed of image will be the same always, i.e. c. The image is said to be "upright", as opposed to inverted. A third characteristic of plane mirror images pertains to the relationship between the object's distance to the mirror and the image's distance to the mirror. For plane mirrors, the object distance is equal to the image distance. Q4. A student has obtained an image of a distant object on a screen to determine the focal length F of the given lens. His teacher after checking the image, gave him another lens of focal length F and asked to focus the same object on the same screen. The student found that to obtain a sharp image he has to move the lens away from the screen. From this finding we may conclude that both the lenses given to the student were:
- Concave and
- Convex and
- Convex and
- Concave and
1 Mark
Ans: 3. Convex and F > F. Explanation: The lens is convex, as it forms real image. As mentioned in the second case, the image distance (v) is increasing; hence, the object distance (u) is decreasing. The lens formula is 1/ F = 1/ v - 1/ u ⇒ F = uv/ u - v For convex lens, object distance = -u Image distance = v ⇒ F = uv/ u + v where F is the focal length of the lens. Therefore, F is lesser for the second lens of focal length F. Hence, F > F. Hence, the correct option is C. Q5. Study the following diagram and select the correct statement about the device 'X':
- Device 'X' is a concave mirror of radius of curvature 12cm.
- Device 'X' is a concave mirror of focal length 6cm.
- Device 'X' is a concave mirror of focal length 12cm.
- Device 'X' is a convex mirror of focal length 12cm.
1 Mark
Ans: 3. Device 'X' is a concave mirror of focal length 12cm. Explanation: From the figure, we can see that the light rays coming from infinity get reflected by the device 'X' and converge at a point at a distance 12cm from it. Therefore, the device 'X' is a concave mirror of focal length 12cm. Q6. A student obtains a sharp image of the distant window (W) of the school laboratory on the screen (S) using the given concave mirror (M) to determine its focal length. Which of the following distances should he measure to get the focal length of the mirror?
1. MW.
2. MS.
3. SW.
4. MW – MS.
1 Mark
Ans: 2. MS.
1 2
F 1 < F 2
F 1 < F 2
F 1 > F 2
F 1 > F 2
1 2
2 1 2
Explanation: To get the focal length of the mirror, the student should measure the distance between mirror and screen because when the object is at infinity, the image is formed at focus i.e. between screen and mirror. So, the distance between screen and mirror should be measured. Q7. A student is using a convex lens of focal length 10 cm to study the image formation by a convex lens for the various positions of the object. In one of his observations, he may observe that when the object is placed at a distance of 20 cm from the lens, its image is formed at (select the correct option):
- 20cm on the other side of the lens and is of the same size, real and erect.
- 40cm on the other side of the lens and is magnified, real and inverted.
- 20cm on the other side of the lens and is of the same size, real and inverted.
- 20cm on the other side of the lens and is of the same size, virtual and erect.
1 Mark
Ans: 3. 20cm on the other side of the lens and is of the same size, real and inverted. Explanation: 20cm on the other side of the lens and is of the same size, real and inverted. Given, focal length of the image, f = 10cm. Thus, the object is placed at 2F (2 × 10 = 20cm). Hence, the image is also formed at 2F. The image will be of same size as that of the object and is real and inverted.
Q8. Beams of light are incident through the holes A and B and emerge out of box through the holes C and D respectively as shown in the Figure. Which of the following could be inside the box?
- A rectangular glass slab.
- A convex lens.
- A concave lens.
- A prism.
1 Mark
Ans: 1. A rectangular glass slab. Explanation: In this case, incident rays fall perpendicularly on the point of incidence. A rectangular glass slab would refract and then re-refract it. Q9. A convex mirror of focal length f forms an image of the size of the object. The distance of the object from the mirror is:
1 Mark
Ans: 3. Explanation: Will use the formula, HERE,
f = +f ; u = –u. (since mirror is convex). So, using those, equation (1) becomes,
(f + u) = nf u = nf – f u = (n - 1) f. Q10. A perfecting reflecting mirror has an area of 1cm. Light energy is allowed to fall on it for an hour at the rate of 10cm. The force that acts on the mirror is:
1 Mark
1 nth n+1n f (n + 1)f (n − 1)f n - 1n f (n − 1)f
m = (^) (f-u)f... (1)
m = + (^1) n;
( (^1) n) = (f+u)f
2
Its image would be formed at 2F. So, the screen needs to be moved towards the lens in order to get a sharp image. Its approximate focal length is 10cm (less than image distance in earlier case). Q16. A man sits in an optician's chair looking into plane mirror which is 2m away from him and views the image of a chart which faces the mirror and is 50cm behind his head. How far away from his eyes does the chart appear to be?
3 Marks
Ans: Distance between the man and the mirror = 2cm. Distance between man and chart = 50cm. = 0.5m. Distance between chart and mirror = 0.5m. + 2m. = 2.5m. Distance between mirror and the image of the chart = 2.5m. Distance between man and the image of chart = Distance between man and the mirror + Distance between mirror and the image of the chart = 2m. + 2.5m. = 4.5m. Q17. A 2.0cm tall object is place perpendicular to the principal axis of a concave lens of focal length 15cm. At what distance from the lens, should the object be placed so that it forms an image 10cm from the lens? Also find the nature and the size of image formed.
3 Marks
Ans: For the object, h = 2cm, f = 10cm, u = -15cm From lens formula,
As v is positive, the image is real. The other aspects about the nature canbe determined from the value of magnification.
Hence, the height of the image is 4cm. This suggests that the image is enlarged. The negative sign of the magnification suggests that the image is inverted. Hence, the image is real, inverted and enlarged. OR Q17. A dentist’s mirror has a radius of curvature of 3cm. How far must it be placed from a small dental cavity to give a virtual image of the cavity that is magnified five times? Ans: R = -3cm (concave mirror) m = (virtual image)
and
We have
The mirror should be placed 1.2cm away from the dental cavity.
Q18. 1. Define focal length of a spherical lens.
- A divergent lens has a focal length of 30 cm. At what distance should an object of height 5 cm from the optical centre of the lens be placed so that its image is formed 15 cm away from the lens? Find the size of the image also.
- Draw a ray diagram to show the formation of image in the above situation.
5 Marks
SECTION-D. LONG ANSWER QUESTION
(^1) v − (^1) u = (^1) f ∴ (^1) v = (^1) f +^1 u (^1) v = 101 + (^) −15 (^1) = 101 − 151 ∴ (^1) v = 3−2 30 = 301 ∴ v = 30cm
m = (^) uv = h
′ h ∴ (^) −15^30 = h
′ 2 ∴ h′^ = −
f = R 2 = 32 = 1.5cm
m = 5 = − vu ⇒ v = −5u (^1) v + (^1) u = (^1) f ⇒ (^) (5u)^1 + (^) u^1 = (−1.5)^1 ⇒ (^) 5u^4 = −1.5^1 ⇒ u = − 4×1.5 5 = −1.2cm
Ans: 1. Optical center of the lens is defined as the point which lies on the principal axis through the rays of light passes without any deflection.
- Given: focal length of convex lens = 20 cm Height of object = 4cm Applying the lens formula:
Therefore u = -20cm Height of image can be caliculated by using the formula:
Therefore, The ray diagram is as follows:
OR
Q18. One-half of a convex lens is covered with a black paper. Will this lens produce a complete image of the object? Verify your answer experimentally. Explain your observations. Ans: The convex lens will form complete image of an object, even if its one half is covered with black paper It can be understood by the following two cases. Case I:
When the upper half of the lens is covered. In this case, a ray of light coming from the object will be refracted by the lower half of the lens. These rays meet at the other side of the lens to form the image of the given object, as shown in the above figure. Case II:
When the lower half of the lens is covered. In this case, a ray of light coming from the object is refracted by the upper half of the lens. These rays meet at the other side of the lens to form the image of the given object, as shown in the above figure. Q19. List the sign conventions that are followed in case of refraction of light through spherical lenses. Draw a diagram and apply these conventions in determining the nature and focal length of a spherical lens which forms three times magnified real image of an object placed 16cm from the lens.
5 Marks
Ans: Sign Convention for Lenses
- Object is always placed to the left of the lens i.e., the light must fall on the lens from left to right.
- All distances parallel to the principal axis are measured from the optical centre of the lens.
- Distances along the direction of incident rays (along positive x -axis) are taken as positive, while distances opposite to the direction of incident rays (along negative x -axis) are taken as negative.
- Distances measured above the principal axis (along positive y -axis) are taken as positive.
(^1) f = (^1) v − (^1) u
−20^1 = −^101 − u^1 (^1) u = − 101 + − 201 (^1) u = − 201
h h (^21) = vu
h 2 = vuh 1 = −10cm−20cm × 4 = 2cm
Ans: 1. (b) No
- (a) Denser to rarer medium
- (a) Away from the normal
- (c) 48.59°
- (c) OR Q20.
The bending of light as it passed from one transparent medium into another is called refraction. Place a pencil in an inclined position in a glass trough and fill three fourth of the trough with water.
- State true or false: The position of the portion of the pencil under water has changed.
- True
- False
- What shall be the reason for the change in the position of the pencil under water?
- Due to reflection
- Due to refraction
- Does the ray of light coming after reflection from the pencil undergo a deviation?
- Yes
- No
- What is the reason for the ray of light coming after reflection from the pencil undergo deviation?
- When light travels from air to air it deviates.
- When light travels from water to air it deviates.
- When light travels from water to oil it deviates.
- None of these
- Is there any change likely to occur if kerosene is used instead of water?
- Pencil appears to be bent less.
- Pencil does not bent.
- Pencil appears to be bent more.
- None of these Ans: 1. (a) True
- (b) Due to refraction
- (a) Yes
- (b) When light travels from water to air it deviates.
- (c) Pencil appears to be bent more. Q21.
Sunil wants to see the micro organisms present in soil. He knows that he needs a microscope to see those tiny things. A microscope is an instrument used to see a small object to look bigger which helps us in a study of many tiny little species. Well, refraction also plays a huge role in the microscope.
- What kind of lens is used in microscope?
4 Marks
n = cv v = nc
n = (^) vc
- Concave lens
- Convex lens
- Bifocal lens
- Plane lens
- The image formed by a convex lens can be.
- Virtual and magnified
- Virtual and diminished
- Virtual and of same size
- Virtual image is not formed
- Absolute refractive index of any medium is always ______.
- Less than 1
- Greater than 1
- 1
- 0
- Power of convex lens is ______.
- Positive
- Positive
- The refracting surfaces obeys the ______.
- Law of reflection
- Law of refraction Ans: 1. (b) Convex lens
- (a) Virtual and magnified
- (b) Greater than 1
- (a) Positive
- (b) Law of refraction Q22.
Abin wanted to see the stars of the night sky. He knows that he needs a telescope to see those distant stars. There are two types of telescopes, reflecting telescopes which are made of mirrors and refracting telescope which are made of lenses. So he decided to take a refracting telescope. There are two lenses, the larger lense gathers and bends the light, while the smaller lens magnifies the image.
- What kind of lenses are used in the refracting telescope?
- Concave lens
- Convex lens
- Bifocal lens
- Both (a) and (b)
- The unit of power of lens is:
- Meter
- Centimeter
- Diopter
- M
- Objective lens will create a ______ image of the object being studied.
- Real
- Virtual
- Eyepiece lens takes the image created by objective lens and ______ it for your viewing.
- Diminishes
- Magnifies
- The lens of a telescope uses a ______ to make things look closer they really are.
- Reflection of light
- Refraction of light
4 Marks
Ans: 1. (b) Convex lens
- (c) Diopter
- (a) Real
- (b) Magnifies
(b) Refraction of light
