VIDEOS
NOTES
ASSIGNMENT
Section A: Multiple Choice Questions (1 mark each)
- According to sign convention, the focal length of a concave mirror is:
a) Always positive
b) Always negative
c) Zero
d) Sometimes positive - If an object is placed in front of a convex mirror, the object distance (u) is:
a) Positive
b) Negative
c) Zero
d) Undefined - The magnification (m) for a real, inverted image is:
a) Positive and greater than 1
b) Positive and less than 1
c) Negative and less than 1
d) Negative and greater than 1 - In the mirror formula 1/f = 1/v + 1/u, all distances are measured from:
a) Center of curvature
b) Focus
c) Pole of the mirror
d) Object - If an image is virtual and erect, the magnification must be:
a) Zero
b) Positive
c) Negative
d) Infinite
Section B: Assertion and Reasoning (2 marks each)
Choose the correct option:
a) Both A and R are true and R is the correct explanation of A
b) Both A and R are true but R is not the correct explanation of A
c) A is true but R is false
d) A is false but R is true
Assertion (A): The focal length of a convex mirror is taken as positive.
Reason (R): The reflected rays appear to diverge from a point behind the mirror.
Assertion (A): The image formed by a concave mirror is real when the object is beyond F.
Reason (R): Real images are always formed on the same side as the object.
Assertion (A): Virtual images have positive image distances (v).
Reason (R): Virtual images are formed on the opposite side of the mirror.
Assertion (A): If magnification is less than 1, the image is diminished.
Reason (R): Magnification is the ratio of image height to object height.
Assertion (A): A positive magnification indicates a real image.
Reason (R): Real images are always upright.
Section C: Fill in the Blanks – Signs and Values (1 mark each)
- For a real image formed by a concave mirror, v = ____, m = ____
- For a virtual, erect image formed by a concave mirror, v = ____, m = ____
- For an object in front of any mirror, u = ____
- For a convex mirror, f = ____, image is always ____
- For an enlarged real image, m = ____, v = ____
Section D: Two Mark Questions – Numericals
- An object is placed 30 cm in front of a concave mirror of focal length 15 cm. Find the position and nature of the image.
- An object 4 cm high is placed in front of a concave mirror. The image formed is 8 cm high and real. Calculate the magnification and image distance if the object is 10 cm from the mirror.
Section E: Three Mark Question
- A concave mirror forms an image twice the size of the object on a screen. If the object is placed 20 cm in front of the mirror, find the position of the image and the focal length of the mirror.
KEY
Section A: Multiple Choice Questions (1 mark each)
- b) Always negative
- b) Negative
- c) Negative and less than 1
- c) Pole of the mirror
- b) Positive
Section B: Assertion and Reasoning (2 marks each)
- a) Both A and R are true and R is the correct explanation of A
- b) Both A and R are true but R is not the correct explanation of A
- a) Both A and R are true and R is the correct explanation of A
- a) Both A and R are true and R is the correct explanation of A
- d) A is false but R is true
Section C: Fill in the Blanks (1 mark each)
- v = negative, m = negative
- v = positive, m = positive
- u = negative
- f = positive, image is always virtual and erect
- m = >1, v = negative
Section D: Two Mark Questions – Numericals
16.
Given:
<u = –30 cm, f = –15 cm (concave mirror)
Using mirror formula:
1/f = 1/v + 1/u
1/–15 = 1/v + 1/(–30)
⇒ –1/15 + 1/30 = 1/v
⇒ –2/30 + 1/30 = –1/30 = 1/v
v = –30 cm
Image is real, inverted and same size
17.
Object height h = +4 cm, Image height h’ = –8 cm (real and inverted),
<u = –10 cm
m = h’/h = –8/4 = –2
m = v/u ⇒ –2 = v/(–10)
⇒ v = 20 cm
Image is real, inverted and enlarged
Section E: Three Mark Question
18.
Given: m = –2 (real, inverted), u = –20 cm
m = v/u ⇒ –2 = v/(–20)
⇒ v = 40 cm
Use mirror formula:
1/f = 1/v + 1/u = 1/40 + 1/(–20) = 1/40 – 1/20 = –1/40
⇒ f = –40 cm
Image is real, enlarged and formed 40 cm in front of mirror
