Light Energy — Practice Quiz
ICSE · Class 8 · Physics
Try a 4-question quiz on Light Energy for ICSE Class 8 Physics: tap an answer to check it and see why. 44 questions in the full chapter test.
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Quick Quiz: Light Energy
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What is the speed of light in air?
When a ray of light travels from air (rarer medium) into glass (denser medium), which direction does it bend?
What is the phenomenon called when white light splits into seven colours on passing through a prism?
What is the correct order of colours in the spectrum of white light from the base of the prism upwards?
Sample Questions
The focal length of a concave mirror is 10 cm. What is its radius of curvature?
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20 cm
The relationship between focal length (f) and radius of curvature (R) is: R = 2 × f. Step 1: Write the formula — R = 2 × f. Step 2: Substitute the value — R = 2 × 10 cm. Step 3: Calculate — R = 20 cm. The radius of curvature is always TWICE the focal length. A common error is to halve the focal length instead of doubling it.
What type of image is ALWAYS formed by a convex mirror, regardless of the position of the object?
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Virtual, erect and diminished
A convex mirror ALWAYS forms a virtual, erect (upright) and diminished (smaller) image, no matter where the object is placed. This is because a convex mirror is a diverging mirror — it spreads reflected rays apart. The image is always formed between the pole and focus, behind the mirror. This property makes it useful as a rear-view mirror in vehicles.
A concave mirror has a radius of curvature of 30 cm. What is its focal length?
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15 cm
The formula connecting focal length and radius of curvature is: f = R/2. Step 1: Write the formula — f = R ÷ 2. Step 2: Substitute — f = 30 cm ÷ 2. Step 3: Calculate — f = 15 cm. The focal length is HALF the radius of curvature. A common mistake is to multiply R by 2 instead of dividing.
Which of the following is the MAIN use of a concave mirror as a shaving mirror?
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It forms an erect and magnified image when the object is close to it
A concave mirror is used as a shaving mirror because when the face (object) is placed between the pole and focus of the mirror, it forms a VIRTUAL, ERECT and MAGNIFIED image. This enlarged image helps in seeing facial features clearly for shaving. If the face were placed beyond the focus, the image would be real and inverted — not useful for shaving!
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