⚡ Grade 9 Science · Physics

Samacheer Class 9 Science - Light

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15 Sections
32 Questions

Complete Grade 9 Science questions and answers for Light. Click any question to expand the answer.

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📋 Sections in this chapter
I. Choose the Correct AnswerII. State Whether True or FalseIII. Fill in the BlanksIV. Match the FollowingV. Assertion and Reason Type QuestionsVI. Answer Very BrieflyVII. Answer BrieflyVIII. Answer in DetailIX. Numerical ProblemsX. Higher Order Thinking SkillsIntext ActivitiesActivity – 1Activity – 2Activity – 3Activity – 4
Your Progress — Light0% complete
1I. Choose the Correct Answer6 questions
Q.1A ray of light passes from one medium to another. Refraction takes place when angle of incidence is▾
✓ Answer
  • (a) (0^\circ)
  • (b) (45^\circ)
  • (c) (90^\circ)

Answer:
(a) (0^\circ), (b) (45^\circ), and all angles except under special cases.

Correction made:
Original answer (90^\circ) was incorrect.
Refraction occurs whenever light enters another medium obliquely or normally due to change in speed.
Q.2______ is used as reflector in torchlight.▾
✓ Answer
  • (a) Concave mirror
  • (b) Plane mirror
  • (c) Convex mirror

Answer:
(a) Concave mirror

Q.3We can obtain enlarged virtual images using▾
✓ Answer
  • (a) concave mirror
  • (b) plane mirror
  • (c) convex mirror

Answer:
(a) Concave mirror

Q.4When the reflecting surface curves outward, the mirror formed is▾
✓ Answer
  • (a) concave mirror
  • (b) convex mirror
  • (c) plane mirror

Answer:
(b) Convex mirror

Q.5When white light passes through a prism, it gets▾
✓ Answer
  • (a) reflected
  • (b) only deviated
  • (c) deviated and dispersed

Answer:
(c) deviated and dispersed

Q.6Speed of light is maximum in▾
✓ Answer
  • (a) vacuum
  • (b) glass
  • (c) diamond

Answer:
(a) vacuum

2II. State Whether True or False5 questions

If false, correct the statement.

Q.1Angle of deviation depends on refractive index of glass.▾
✓ Answer

Answer: True

Q.2If light passes obliquely from one medium to another, it suffers no deviation.▾
✓ Answer

Answer: False

Correct Statement:
A ray passing obliquely from one medium to another bends due to refraction.

Q.3Convex mirror always forms virtual, erect and diminished image.▾
✓ Answer

Answer: True

Q.4When object is at centre of curvature of concave mirror, image formed is virtual and erect.▾
✓ Answer

Answer: False

Correct Statement:
Image formed is real, inverted and same size.

Q.5Brilliance of diamonds is due to total internal reflection.▾
✓ Answer

Answer: True

3III. Fill in the Blanks0 questions
  • When light travels from rarer to denser medium, it bends towards the normal.
  • The mirror used in searchlights is concave mirror.
  • Angle of deviation in a prism depends on the angle of incidence.
  • Radius of curvature of a concave mirror with focal length 5 cm is 10 cm.
$$R = 2f$$
  • Large concave mirrors are used in solar furnaces to concentrate sunlight.
4IV. Match the Following0 questions
StatementConcept
Ratio of image height to object heightMagnification
Used in hairpin bendsConvex mirror
Coin appearing raised in waterRefraction
MirageTotal internal reflection
Dentist’s mirrorConcave mirror
5V. Assertion and Reason Type Questions2 questions
Q.1Question 1▾
✓ Answer

Assertion:
Plane mirror is preferred over convex mirror at hairpin bends.

Reason:
Convex mirror has larger field of view.

Answer:
(d) Assertion is false but reason is true.

Convex mirrors are actually used at hairpin bends.
Q.2Question 2▾
✓ Answer

Assertion:
A ray directed towards centre of curvature retraces its path after reflection.

Reason:
Angle of incidence = angle of reflection = (0^\circ)

Answer:
(a) Both are true and reason correctly explains assertion.

6VI. Answer Very Briefly6 questions
Q.1Which mirror has negative focal length according to Cartesian sign convention?▾
✓ Answer

Answer:
Concave mirror.

Q.2Which mirror gives▾
✓ Answer
(i) erect and enlarged image?

Concave mirror.

(ii) same-sized inverted image?

Concave mirror (when object is at centre of curvature).

Q.3If object is placed at focus of concave mirror, where is image formed?▾
✓ Answer

Answer:
At infinity.

Q.4Why does light bend when it travels from one medium to another?▾
✓ Answer

Answer:
Light bends because its speed changes in different media.

This bending is called:

Refraction

Q.5What is speed of light in vacuum?▾
✓ Answer

Answer:

$$3 \times 10^8 , m/s$$
Q.6Why do dentists use concave mirrors?▾
✓ Answer

Answer:
Concave mirrors produce magnified, erect images when object is placed between pole and focus.

This helps dentists observe teeth clearly.

7VII. Answer Briefly5 questions
Q.1Image Formation by Concave Mirror▾
✓ Answer

Nature of Image:

  • Real
  • Inverted
  • Magnified

(when object is between C and F)

Q.2Identify Concave and Convex Mirrors▾
✓ Answer
Concave MirrorConvex Mirror
Dentist’s mirrorRear-view mirror
Torchlight reflectorShopping mall mirrors
Make-up mirror
Q.3Direction of Incident Ray That Retraces Path▾
✓ Answer

Answer:
Ray directed through centre of curvature retraces path.

Reason:

It strikes mirror normally.

$$i = r = 0^\circ$$
Q.4Define Magnification▾
✓ Answer

Answer:

Magnification is ratio of image height to object height.

$$m = \frac{h_i}{h_o}$$

Also,

$$m = -\frac{v}{u}$$

Where:

  • (h_i) = image height
  • (h_o) = object height
  • (v) = image distance
  • (u) = object distance

Sign Convention:

  • Negative → real image
  • Positive → virtual image
Q.5Mirror Formula▾
✓ Answer
$$\frac{1}{f} = \frac{1}{v} + \frac{1}{u}$$

Where:

  • (f) = focal length
  • (u) = object distance
  • (v) = image distance
8VIII. Answer in Detail2 questions
Q.1Image Formation by Concave Mirror▾
✓ Answer

(i) Object at C

Image:

  • At C
  • Real
  • Inverted
  • Same size

(ii) Object Between C and F

Image:

  • Beyond C
  • Real
  • Inverted
  • Magnified

(iii) Object Between F and P

Image:

  • Behind mirror
  • Virtual
  • Erect
  • Magnified
Q.2Refraction of Light▾
✓ Answer

# (a) Rarer to Denser Medium

Light bends towards normal.

Example:
Air → Glass

# (b) Denser to Rarer Medium

Light bends away from normal.

Example:
Glass → Air

# (c) Light Incident Normally

When incident ray falls normally:

$$i = 0^\circ$$

No deviation occurs.

9IX. Numerical Problems3 questions
Q.1Concave Mirror Magnification▾
✓ Answer

Given:

$$m = -3$$

(real image)

$$u = -7cm$$

Using:

$$m = -\frac{v}{u}$$
$$-3 = -\frac{v}{-7}$$
$$v = -21cm$$

Answer:

Image forms 21 cm in front of mirror.

Q.2Speed of Light in Glass▾
✓ Answer

Given:

$$\mu = 1.5$$
$$c = 3 \times 10^8 m/s$$

Using:

$$\mu = \frac{c}{v}$$
$$v = \frac{3 \times 10^8}{1.5}$$
$$v = 2 \times 10^8 m/s$$
Q.3Refractive Index of Water▾
✓ Answer

Given:

$$v = 2.25 \times 10^8 m/s$$
$$c = 3 \times 10^8 m/s$$

Using:

$$\mu = \frac{c}{v}$$
$$\mu = \frac{3}{2.25}$$
$$\mu = 1.33$$
10X. Higher Order Thinking Skills3 questions
Q.1Light Emerging from Water to Air▾
✓ Answer

Observation:

Light bends away from normal when moving from denser to rarer medium.

Q.2Refraction from Air to Glass▾
✓ Answer

Answer:

Since glass is optically denser than air, light bends towards normal.

Therefore:

$$r < i$$

Angle of refraction is less than angle of incidence.

Q.3Speed of Light in Diamond▾
✓ Answer

Given:

$$\mu = 2.41$$

Using:

$$\mu = \frac{c}{v}$$
$$v = \frac{3 \times 10^8}{2.41}$$
$$v = 1.24 \times 10^8 m/s$$

Conclusion:

Speed of light in diamond is much lower than in vacuum.

11Intext Activities0 questions
12Activity – 10 questions

Height of Mirror Needed

Observation:

To see full body:

$$\text{Height of mirror} = \frac{\text{Height of person}}{2}$$
13Activity – 20 questions

Burning Paper Using Concave Mirror

Observation:

Paper burns when placed at focus.

Reason:

Concave mirror concentrates sunlight at focus, producing intense heat.

14Activity – 30 questions

Image in Convex Mirror

Observation:

  • Image is virtual
  • Erect
  • Diminished

As object moves away, image becomes smaller.

15Activity – 40 questions

Pencil Appearing Bent in Water

Observation:

Pencil appears bent at water surface.

Reason:

Due to refraction of light at air-water interface.

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