Reviewing SCERT Class 8 Basic Science Solutions and Kerala Syllabus Class 8 Basic Science Chapter 12 Spherical Mirrors Question Answer Notes Pdf can uncover gaps in understanding.
Class 8 Basic Science Chapter 12 Spherical Mirrors Question Answer Notes
Class 8 Basic Science Chapter 12 Notes Kerala Syllabus Spherical Mirrors Question Answer
Spherical Mirrors Class 8 Questions and Answers Notes
Let’s Assess
Question 1.
A concave mirror has a focal length of 30 cm. Find out its radius of curvature.
Answer:
Given: Focal length (f) = 30 cm
Formula: The focal length (f) is half of the radius of curvature (R).
f = R/2 Calculation:
R = 2f
R = 2 × 30 cm
R = 60 cm
The radius of curvature is 60 cm.
Question 2.
OA is a ray incident obliquely on a concave mirror. Draw and mark the path of its reflected ray. Write on what basis you marked this like.
Answer:
The Law of Reflection.
- In this case, the light ray (OA) is striking the pole (P) of the mirror.
- At the pole, the principal axis itself acts as the normal (the 90° line).
- According to the law of reflection, the angle of incidence (i) must be equal to the angle of reflection (r). Therefore, the reflected ray will travel down wards at the same angle to the principal axis as the incident ray.
Question 3.
Write what type of spherical mirrors should be used to obtain images with the following characteristics:
a. Real, smaller than the object
b. Virtual, smaller than the object
c. Real, larger than the object
d. Virtual, larger than the object
Answer:
a. Concave Mirror.
Reason: This happens when the object is placed beyond C or at infinity.)
b. Convex Mirror.
Reason: A convex mirror always forms a virtual, erect, and small image, regardless of the object’s position.)
c. Concave Mirror.
Reason: This happens when the object is placed between C and F.)
d. Concave Mirror.
Reason: This is the special case used for makeup or shaving mirrors, where the object is placed between F and P.)
Question 4.
Observe the picture.
a) If the object shown in the picture is replaced with an object of 6 cm height at the same position, what will be the height of the image?
b) If the distance of the object from the mirror was 30 cm and an image of the same size as the object was obtained on the screen, what is the focal length of the mirror?
Answer:
a. m = \(\frac{h_1}{h_0}\) = \(\frac{6 \mathrm{~cm}}{3 \mathrm{~cm}}\) = -2
m = \(\frac{h_1}{h_0}\)
h1 = m × h0
= -2 × 6
= -12 cm
b. If image is same size that of object. The object will be at C
∴ object distance = 30
R = 30 cm
f = \(\frac{R}{2}\) = \(\frac{30}{2}\) = 15 cm
Basic Science Class 8 Chapter 12 Question Answer Kerala Syllabus
Textbook Page No : 203
Question 1.
What is special about the mirror in his hand (Fig. 12.1)?
Answer:
The mirror is a concave mirror (a type of spherical mirror). It is special be-cause it makes the person’s reflection (image) appear slightly larger than the object.
Question 2.
Can you see your face in it (The flat, silver paper on cardboard)?
Answer:
Yes, you can see your face. An image is formed when light reflects off a smooth surface like the silver paper.
Textbook Page No : 204 & 205
Question 3.
What change do you notice in the image when you bend the cardboard inward?
Answer:
When bent inward (acting as a concave mirror), the image changes and can become inverted, or larger and erect if held very close.
Question 4.
What if you bend it outward?
Answer:
When bent outward (acting as a convex mirror), the image will appear erect and smaller (diminished).
Question 5.
Complete Table 12.1: Characteristics of the image
Answer:
| Shape of the sheet | Characteristics of the image |
| Flat (Plane Mirror) | Erect, Same size as the object, Virtual. |
| Bend outward (Convex Mirror) | Erect, Smaller than the object, Virtual. |
| Bend inward (Concave Mirror – close range) | Erect, Larger (Magnified) than the object, Virtual. |
Question 6.
How does the image appear on the outer side of the spoon?
Answer:
The outer side acts as a convex mirror, forming an image that is Erect, Virtual, and Smaller.
Question 7.
What about the inner side?
Answer:
The inner side acts as a concave mirror. If you hold it close, the image is Erect, Virtual, and Larger. If you hold it further away, the image is Inverted, Real, and Smaller.
Question 8.
How the images formed on curved surfaces differ from those formed by plane mirrors.
Answer:
- Plane Mirrors: form an image that is always erect, virtual, and the same size.
- Curved Surfaces (Spherical Mirrors) can form images that are real or virtual, inverted or erect, and smaller, the same size, or larger than the object.
Question 9.
Do the reflected rays converge at a point (Ice Cream Ball-Inner Surface/ Concave Mirror)?
Answer:
Yes, the reflected rays converge to a single point called the principal focus.
Question 10.
What difference do you observe now (Ice Cream Ball-Outer Surface/Convex Mirror)?
Answer:
The reflected rays diverge (spread out) and do not meet. They appear to come from a point behind the mirror.
Textbook Page No : 206
Question 11.
Complete Table 12.2 (Law of Reflection in Spherical Mirrors)
Answer:
In spherical mirrors, the angle of incidence (i) is equal to the angle of reflection (r).
| SI No | Angle of incidence (i) (Degree) | Angle of reflection (r) (Degree) |
| 1 | 30 | 30 |
| 2 | 40 | 40 |
| 3 | 60 | 60 |
Textbook Page No : 208
Question 12.
The principal focus of a convex mirror is virtual. Why?
Answer:
The principal focus is virtual because the light rays that fall parallel to the principal axis do not actually meet after reflection; they only appear to diverge from a point behind the mirror. Since the rays do not converge at this point, the image or focus cannot be caught on a screen.
Question 13.
What would be the radius of curvature of a concave mirror with a focal length of 40 cm?
Answer:
The relationship is: R = 2f (Radius of curvature is twice the focal length)
R = 2 × 40 cm
R = 80 cm
Question 14.
What are the characteristics of the images formed by plane mirrors?
Answer:
The characteristics are: Erect and Virtual. The image is also the same size as the object.
Textbook Page No : 209
Question 15.
Write down the characteristics of the image of a distant object formed on the wall with a concave mirror.
Answer:
The image is formed at the principal focus (F). The characteristics are:
- Smaller than the object (Highly diminished)
- Inverted
- Real
Question 16.
At what position is the screen placed to get a clear image?
Answer:
For a Convex Mirror, a clear, real image can never be obtained on a screen because a convex mirror always forms a virtual image behind the mirror.
Question 17.
What are the characteristics of the image?
Answer:
When a concave mirror is used to form the image of a distant object (like the sun or a far-off tree), and the screen is placed at the Principal Focus (F).
- Nature: Real (can be formed on a
- Orientation: Inverted (upside down), as a tiny, bright point).
- Size: Highly Diminished (much, much smaller than the object—it appears as a tiny, bright point).
- Position: At the Principal Focus (F). them.
Textbook Page No : 210
Question 18.
Complete Table 12.3: Concave Mirror Image Formation.
Answer:
| SI No | Position of the object | Position of the image | Characteristics of the image |
| 1 | Very far (at infinity) | At F (Principal Focus) | Small, Inverted, Real |
| 2 | Beyond C (Centre of Curvature) | Between F and C | Small (Diminished), Inverted, Real |
| 3 | At C | At C | Same size, Inverted, Real |
| 4 | Between C and F | Beyond C | Large (Magnified), Inverted, Real |
| 5 | At F | At infinity | Highly magnified. Inverted, Real |
| 6 | Between F and P (Pole) | Behind the mirror | Large (Magnified), Erect, Virtual |
Question 19.
Could the analysis of this table provide the answer to the question related to the introduction picture of this unit?
Answer:
Yes. The mirror in the introduction makes the face appear slightly larger. This corresponds to the case in SI No. 6 (Object Between F and P), which is a characteristic of a concave mirror.
Question 20.
What are the characteristics of the mirror that reflects your face at a spectacle shop? Why does the face appear larger?
Answer:
It is a Concave Mirror.
Reason: Based on Table 12.3 (Row 6), a concave mirror ¡s the only mirror that can produce a large, erect, and virtual image.
This happens when the object (the face) is placed very close to the mirror, “Between F and P”. This is often used as a shaving mirror or makeup mirror.
Question 21.
Are the same types of images formed in a convex mirror?
Answer:
No. Concave mirrors form both real and virtual images, while a convex mirror forms only one type of image.
Question 22.
Can you see the image?
Answer:
Yes, you can see the image by looking into the mirror.
Question 23.
Can you project it on a screen?
Answer:
No. The image formed is Virtual, meaning it cannot be caught on a screen.
Question 24.
Characteristics of the Image Formed (Complete the list):
Answer:
A convex mirror always forms an image that is:
- Erect
- Small (Diminished)
- virtual
- Always between the principal focus (F) and the pole (P)
Textbook Page No : 211 & 213
Textbook Page No : 213 & 214
Complete the image formation for the remaining positions:
• Object is Beyond C:
Position of the image: Between C and F (C യ്ക്കും F നും ഇടയിൽ)
Characteristics of the image:
- Inverted (തലകീഴായത്)
- Smaller than the object (ചെറുത്)
- Real (യഥാർത്ഥം)
• Object is to C:
Position of the image: At C (C-യിൽ)
Characteristics of the image:
- Inverted (തലകീഴായത്)
- Same size as the object (ഒരേ വലിപ്പം)
- Real (യഥാർത്ഥം)
• Object between C and F (C യ്ക്കും F നും ഇടയിൽ)
Position of the image: Beyond C (C-ക്ക് അപ്പുറം)
Characteristics of the image:
- Inverted (തലകീഴായത്)
- Larger than the object (വലുത്)
Real (യഥാർത്ഥം)
• Object at F (F – ൽ)
Position of the image: At infinity (അന ന്തതയിൽ)
Characteristics of the image:
- Inverted (തലകീഴായത്)
- Very large (വളരെ വലുത്)
- Real (യഥാർത്ഥം)
• Object between F and P (F-നും P-നും P-യ്ക്കും ഇടയിൽ)
Position of the image: Behind the mirror (ദർപ്പണത്തിന് പിന്നിൽ)
Characteristics of the image:
- Erect (നിവർന്നത്)
- Larger than the object (വലുത്)
- Virtual (മിഥൃ)
• Discuss the characteristics of real and virtual images and complete the table given below.
Answer:
| Real Image | Virtual Image |
| Inverted | Erect |
| Can be caught on a screen | Cannot be caught on a screen |
| Formed in front of the mirror | Formed behind the mirror |
| Formed by the actual intersection of reflected rays | Formed where reflected rays appear to intersect |
Class 8 Basic Science Chapter 12 Question Answer Extended Activities
Question 1.
Present a seminar on the uses of spherical mirrors in daily life and the devices that include spherical mirrors.
Answer:
Torches/Flashlights – Concentrates the light from a small bulb into a powerful, straight beam to illuminate distant objects.
Headlights of Cars Generates a strong, parallel beam to provide maximum visibility on the road.
Searchlights – Used in defense, rescue operations, and stage lighting to project a high-intensity beam over long distances.
Spherical Mirrors Class 8 Notes
Class 8 Basic Science Spherical Mirrors Notes Kerala Syllabus
Curved mirrors
A smooth curved surface can also form images like a plane surface. (നിരപ്പായ ദർപ്പണങ്ങൾ), which we use every day. However, images can also be formed by curved surfaces.
Spherical Mirrors (ഗോളീയ ദർപ്പണങ്ങൾ)
Mirrors whose reflecting surface forms a part of a sphere are called spherical mirrors.
ഒരു ഗോളത്തിന്റെ (sphere) ഭാഗമായ ദർപ്പണങ്ങ ളെയാണ് (mirrors) ഗോളീയ ദർപ്പണങ്ങൾ എന്ന് പറയുന്നത്. ഒരു സ്പൂണിന്റെ ഉൾഭാഗവും പുറംഭാ ഗവും ഗോളീയ ദർപ്പണങ്ങൾക്ക് ഉദാഹരണമാണ്.
Types of Spherical Mirrors
There are two main types of spherical mirrors:
Concave Mirror (കോൺകേവ് ദർപ്പണം)
Spherical mirrors with a reflecting surface curved inward are called concave mirrors.
Example: The inner side of a spoon (“cave” side) or the mirror in Fig. 12.9.
Property: A concave mirror generally converges (ഒരു ബിന്ദുവിലേക്ക് അടുപ്പിക്കുന്നു) light rays that fall on it.
Convex Mirror (കോൺവെക്സ്)
Spherical mirrors with a reflecting surface curved outward are called convex mirrors.
Example: The outer side of a spoon or the mirror in Fig. 12.10.
Property: A convex mirror generally diverg- es (വിവിധ ദിശകളിലേക്ക് അകറ്റുന്നു) light rays
that fall on it.
Important Terms for Spherical Mirrors
Centre of Curvature (C) (വക്രതാ കേന്ദ്രം):
- A spherical mirror is part of an imaginary sphere. The centre of this sphere is called the centre of curvature.
- It is represented by the letter C in diagrams.
Radius of Curvature (R) (വക്രതാ ആരം):
- The radius of the imaginary sphere of which the mirror is a part.
- In Fig. 12.9 & 12.10, the lines CP, CB, and CA all represent the radius of curvature.
Pole (P) (പോൾ):
- The midpoint of the reflecting surface of the spherical mirror.
- It is represented by the letter P in diagrams.
Aperture
- The diameter of the circular reflecting surface of a spherical mirror.
- In Fig. 12.9, the distance from A to B (along the curve) represents the reflecting surface, and its diameter is the aperture.
Principal Axis(മുഖ്യ അക്ഷം):
- The imaginary straight line connecting the centre of curvature (C) and the pole (P) of the mirror.
- C (വക്രതാ കേന്ദ്രം); ദർപ്പണം ഏത് ഗോളത്തി ന്റെ ഭാഗമാണോ, ആ ഗോളത്തിന്റെ കേന്ദ്രം.
- R (വകതാ ആരം): ആ ഗോളത്തിന്റെ ആരം (radius).
- P (പോൾ): ദർപ്പണത്തിന്റെ പ്രതിപതിക്കുന്ന പ തലത്തിന്റെ (reflecting surface)മധ്യബിന്ദു.
- (മുഖ്യ അക്ഷം). C-യെയും P-യെയും തമ്മിൽ ബന്ധിപ്പിക്കുന്ന നേർ രേഖ.
Reflection in Spherical Mirrors (ഗോ ളീയ ദർപ്പണങ്ങളിലെ പ്രതിപതനം)
The laws of reflection that apply to plane mirrors are also applicable to spherical mirrors.
- The Law of Reflection: For all mirrors, the angle of incidence (i) is equal to the angle of reflection (r).
- The activity in Fig. 12.11 confirms this. If you shine a ray at an angle of 30°, it will reflect at 30°.
ഒരു നിരപ്പായ കണ്ണാടി (plane mirror) പോലെ mom, conglo Borgen (spherical mirrors) പ്രകാശത്തിന്റെ പ്രതിപതന നിയമങ്ങൾ (laws of reflection) ബാധകമാണ്. അതായത്, പ തിക്കുന്ന കോണും (angle of incidence) പ്ര തിപതന കോണും (angle of reflection) എപ്പോ ഴും തുല്യമായിരിക്കും.
Principal Focus (F) and Focal Length (f)
This is a very important property that defines how a mirror bends light.
Concave Mirror (കോൺകേവ് ദർപ്പണം)
- In a concave mirror, light rays that fall parallel to the principal axis converge (ഒത്തുചേരുന്നു) to a single point on the principal axis after reflection. This point is called the principal focus (F).
- Real Focus: The focus of a concave mirror is Real ((യഥാർത്ഥം)). This is because the light rays actually meet at that point. You can prove this by holding a paper at F and seeing the light converge to a bright spot.
- Convex Mirror (കോൺവെക്സ് ദർപ്പണം)
- In a convex mirror, light rays that fall parallel to the principal axis appear to diverge (അകന്നുപോകുന്നു) from a particular point on the principal axis after reflection. This point is called the principal focus (F).
- Virtual Focus: The focus of a convex mirror is Virtual (മിഥു). This is because the rays do not actually meet; they only appear to be coming from a point behind the mirror.
Focal Length (f) (ഫോക്കസ് ദൂരം)
• The distance from the pole (P) of the mirror to the principal focus (F) is called the focal length (f).
Relationship between Focal Length (f) and Radius of Curvature (R)
For spherical mirrors, the focal length is exactly half of its radius of curvature.
Formula: f = R/2
Image Formation in Spherical Mirrors Using Ray Diagrams (ചിത്രങ്ങൾ ഉപയോഗിച്ച് പ്രതിബിംബ രൂപീകരണം)
To find the position and nature of an image, we can draw ray diagrams. These diagrams use a few simple rules for rays of light, all based on the law of reflection (∠i = ∠r).
Any line drawn from the Centre of Curvature (C) to the mirror is perpendicular (normal) to the mirror’s surface at that point.
The 4 Rules for Drawing Ray Diagrams:
Image Formation by a Concave Mirror
• Object is at infinity (വസ്തു അനന്തതയിൽ)
• Position of the image: At F (ഫോക്കസിൽ)
Characteristics of the image:
- Inverted (തലകീഴായത്)
- Smaller than the object (വളരെ ചെറുത്)
- Real (യഥാർത്ഥം)
• Object is Beyond C:
Position of the image: Between C and F (Cയ്ക്കും Fനും ഇടയിൽ)
Characteristics of the image:
- Inverted (തലകീഴായത്)
- Smaller than the object (ചെറുത്)
- Real (യഥാർത്ഥം)
• Object is at C:
Position of the image: At C (C-യിൽ)
Characteristics of the image:
- Inverted (തലകീഴായത്)
- Same size as the object (ഒരേ വലിപ്പം)
- Real (യഥാർത്ഥം)
• Object between C and F (C-യ്ക്കും Fനും ഇടയിൽ)
Position of the image: Beyond C (C-ക്ക് അപ്പുറം)
Characteristics of the image:
- Inverted (തലകീഴായത്)
- Larger than the object (വലുത്)
- Real (യഥാർത്ഥം)
• Object at F (F – ൽ)
Position of the image: At infinity (അനന്തതയിൽ)
Characteristics of the image:
- Inverted (തലകീഴായത്)
- Very large (വളരെ വലുത്)
- Real (യഥാർത്ഥം)
• Object between F and P (F-നും P-നും P-യ്ക്കും ഇടയിൽ)
Position of the image: Behind the mirror (ദർപ്പണത്തിന് പിന്നിൽ)
Characteristics of the image:
- Erect (നിവർന്നത്)
- Larger than the object (വലുത്)
- Virtual (മിഥു)
| Position of the object | Position of the image | Size of the image | Nature of the image |
| At infinity | At the focus F | Highly diminished, point-sized | Real and inverted |
| Beyond C | Between F and C | Diminished | Real and inverted |
| AtC | AtC | Same size | Real and inverted |
| Between C and F | Beyond C | Enlarged | Real and inverted |
| At F | At infinity | Highly enlarged | Real and inverted |
| Between P and F | Behind the mirror | Enlarged | Virtual and erect |
Image Formation by a Convex Mirror
Convex mirrors are simpler. No matter where the object is placed in front of it, the image is always the same type.
Characteristics of the image:
- Virtual
- Erect
- Smaller than the object
Real Images vs. Virtual Images (യഥാർത്ഥവും മിഥ്യയുമായ പ്രതിബിം)
Real Images: These are images that can be caught on a screen (e.g., the image of a candle formed on the white screen in Fig. 12.14). Real images are typically inverted (തലകീഴായവ).
Virtual Images: These are images that can- not be caught on a screen (e.g., the image you see of yourself in a plane mirror). Virtual images are typically erect (നിവർന്നവ).
| Real Image | Virtual Image |
| Inverted | Erect |
| Can be caught on a screen | Cannot be caught on a screen |
| Formed in front of the mirror | Formed behind the mirror |
| Formed by the actual intersection of reflected rays | Formed where reflected rays appear to intersect |
ഒരു സ്ക്രീനിൽ (Screen) പതിപ്പിക്കാൻ കഴിയുന്ന പ്രതിബിംബങ്ങളെ യഥാർത്ഥ പ്രതിബിംബം (Real Image) എന്ന് പറയുന്നു. സ്ക്രീനിൽ പതിപ്പിക്കാൻ കഴിയാത്തതും, ദർപ്പണത്തിനുള്ളിൽ കാണുന്നതു മായ പ്രതിബിംബങ്ങളെ മിഥ്യാ പ്രതിബിംബം (Virtual Image) എന്ന് പറയുന്നു.
Magnification (ആവർധനം)
The size of the image formed by a spherical mirror changes depending on the object’s position. Magnification is the measure of how large or small the image is compared to the object.
The ratio of the height of the image (h) to the height of the object (h) is called magnification (m).
Formula:
m = \(\frac{\text { Height of the image }}{\text { Height of the object }}\) = \(\frac{h_1}{h_0}\)
Sign Convention for Magnification:
To know if the image is erect (നിവർന്നത്) or inverted (തലകീഴായത്), we use a sign convention:
- Measurements above the principal axis (like an erect object or erect image) are considered positive (+).
- Measurements below the principal axis (like an inverted image) are considered. negative (-).
Interpreting the value of ‘m’:
- If m is negative (-): The image is invert- ed and real.
- If m is positive (+): The image is erect and virtual.
- If the value of m is greater than 1 (e.g., 2, -3): The image is larger (magnified). If the value of m is less than 1 (e.g., 0.5, -0.4): The image is smaller (diminished).
ആവർധനം (m) എന്നത് പ്രതിബിംബത്തിന് വസ് തുവിനേക്കാൾ എന്ത് വലിപ്പമുണ്ട് എന്ന് കാണിക്കു ന്ന ഒരു സംഖ്യയാണ്.
m ഒരു പോസിറ്റീവ് (+) സംഖ്യയാണെങ്കിൽ, പ്രതി ബിംബം നിവർന്നതും (erect) മിഥ്യയും (virtual) ആയിരിക്കും.
m ഒരു നെഗറ്റീവ് (-) സംഖ്യയാണെങ്കിൽ, പ്രതിബിം ബം തലകീഴായതും (inverted) യഥാർത്ഥവും (real) ആയിരിക്കും.
Uses of Spherical Mirrors in Daily Life (ഗോളീയ ദർപ്പണങ്ങളുടെ ഉപയോഗങ്ങൾ)
Spherical mirrors have many uses in our daily life.
Uses of Concave Mirrors (കോൺകേവ് ദർപ്പ ണത്തിന്റെ ഉപയോഗങ്ങൾ)
Concave mirrors are used when we need to converge light or get a magnified image.
• Shaving Mirror / Makeup Mirror / Dentist’s Mirror:
When an object (like a face or a tooth) is placed very close to the mirror (between the pole P and focus F), a concave mirror forms an enlarged, erect, and virtual image. This allows for a clear, magnified view.
• Flashlights and Vehicle Headlights:
Light rays that start from the principal focus (F) will, after reflection, travel parallel to the principal axis. The bulb is placed exactly at the focus (F) to produce a strong, parallel beam of light that can travel a long distance.
• Solar Thermal Power Plants Large concave mirrors (or reflectors) are used to collect sunlight. Rays of light from the sun (a distant object) come parallel to the principal axis and converge at the principal focus (F) after reflection. This concentrates a huge amount of solar energy at one point, generating intense heat to create steam.
Uses of Convex Mirrors (കോൺവെക്സ് ദർപ്പണത്തിന്റെ ഉപയോഗങ്ങൾ)
Convex mirrors are used when we need to diverge light or get a wider field of view.
• Rear-view/Side-view Mirrors in Vehicles:
Reason: A convex mirror always forms a small, erect, and virtual image. Because the image is small, it can cover a much wider field of view than a plane mirror, allowing the driver to see more of the road and traffic behind them.
Warning: “OBJECTS IN THE MIRROR ARE CLOSER THAN THEY APPEAR”. This warning is needed because the small, diminished image can make our brain think the car behind is farther away than it actually is.
• Road Safety Mirrors (on sharp turns):
Reason: Large convex mirrors are placed on blind corners and sharp turns so drivers can see oncoming traffic from beyond the curve, helping to reduce accidents.
• Reflectors in Street Lamps:
Reason: A convex mirror is placed above the bulb to diverge (spread) the light rays over a wider area of the street.