If your image appears to be erect, no matter how far you stand from a mirror, the mirror is likely to be :
- A.Plane
- B.Concave
- C.Convex
- D.Either plane or convex
Correct answer
Explanation
The correct answer is D, Either plane or convex. Both a plane mirror and a convex mirror always form an erect, virtual image, whatever the distance of the object.
A plane mirror forms an image of the same size, as far behind the mirror as the object is in front of it, and it is always erect. A convex mirror always forms a virtual, erect and diminished image between its pole and focus, which is why it is used as a rear-view mirror in vehicles. Only a concave mirror changes its behaviour with distance: it gives an erect, enlarged image when the object is between the pole and the focus, and an inverted, real image beyond the focus.
A is wrong: a plane mirror fits, but so does a convex mirror, so A is incomplete.
B is wrong: a concave mirror gives inverted images once you stand beyond its focus.
C is wrong: a convex mirror fits, but it is not the only one.
Exam tip: always erect = plane and convex mirror; concave mirror erect only when the object is within the focus (shaving and make-up mirrors).
Practice Questions
View allBronze is an alloy of copper and
- A.nickel
- B.iron
- C.tin
- D.aluminium
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Bronze is an alloy of copper and tin, usually about 88 parts copper to 12 parts tin. Adding tin makes copper harder, stronger and easier to cast, and bronze also resists corrosion well.
Read the full explanation →Which one of the following instruments is used for measuring moisture content of air?
- A.Hydrometer
- B.Hygrometer
- C.Hypsometer
- D.Pycnometer
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A hygrometer measures humidity, that is, the amount of water vapour or moisture in the air. The name comes from the Greek "hygros", meaning wet.
Read the full explanation →Which one of the following elements is present in the green pigment of leaves?
- A.Magnesium
- B.Iron
- C.Calcium
- D.Copper
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The green pigment of leaves is chlorophyll, and a magnesium atom sits at the centre of every chlorophyll molecule.
Read the full explanation →Consider the following actions :
1. Detection of car crash/collision which results in the deployment of airbags almost instantaneously
2. Detection of accidental free fall of a laptop towards the ground which results in the immediate turning off of the hard drive
3. Detection of the tilt of the smartphone which results in the rotation of display between portrait and landscape mode
In how many of the above actions is the function of accelerometer required?
- A.Only one
- B.Only two
- C.All three
- D.None
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An accelerometer measures acceleration, including the pull of gravity, and each of the three actions depends on reading it. An accelerometer is a small sensor, today usually a MEMS (micro-electro-mechanical system) chip, that senses changes in speed and the direction of gravity.
Read the full explanation →Consider the following statements :
1. Carbon fibres are used in the manufacture of components used in automobiles and aircrafts.
2. Carbon fibres once used cannot be recycled.
Which of the statements given above is/are correct?
- A.1 only
- B.2 only
- C.Both 1 and 2
- D.Neither 1 nor 2
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Carbon fibre is widely used in cars and aircraft for its strength and low weight, and it can be recovered and recycled.
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