Which one of the following statements is correct for a plane mirror?
- A.Its focal length is zero.
- B.The size of the image of an object placed in front of the mirror is slightly less than that of the object.
- C.The image is virtual, erect and laterally inverted.
- D.Its focal length is 200 cm.
Correct answer
Explanation
The correct answer is C, The image is virtual, erect and laterally inverted. A plane mirror always forms an image that stands upright, cannot be caught on a screen, and has its left and right sides swapped.
In a plane mirror, reflected rays never actually meet; they only appear to come from a point behind the mirror, so the image is virtual. The image is as far behind the mirror as the object is in front of it and is exactly the same size, so magnification is 1. Lateral inversion is why the word AMBULANCE is painted in mirror writing on the front of ambulances, so drivers ahead read it correctly in their mirrors.
A is wrong because a plane mirror can be treated as a sphere of infinite radius, so its focal length is infinite, not zero. B is wrong because the image is exactly the same size as the object. D is wrong because a plane mirror has no finite focal length.
Exam tip: plane mirror image is virtual, erect, same size, laterally inverted, focal length infinity.
Practice Questions
View allThe correct order of atomic radius of Li, Na, Be and O is
- A.Na > Li > Be > O
- B.Na > Be > Li > O
- C.Be > Li > Na > O
- D.O > Be > Li > Na
Show answer
Two trends of the periodic table decide the order. Going down a group, atomic radius increases because each new period adds an electron shell; so sodium, in period 3, is larger than lithium, in period 2, of the same group 1.
Read the full explanation →Why does the Rough Endoplasmic Reticulum look 'rough' under a microscope ?
- A.Due to the presence of ribosomes on its surface
- B.Due to the absence of ribosomes on its surface
- C.Due to the presence of lysosomes on its surface
- D.Due to the presence of mitochondria on its surface
Show answer
The endoplasmic reticulum (ER) is a network of membrane tubes and sacs inside the cell. Part of it is studded on the outside with tiny granules called ribosomes, which give it a dotted, rough look under an electron microscope; this part is the rough ER.
Read the full explanation →An aqueous solution of an acid conducts electricity. This is because
- A.It contains hydrogen ion
- B.It contains water molecules
- C.Electricity passes through it
- D.It generates electricity
Show answer
When an acid such as hydrochloric acid dissolves in water, it splits into ions: hydrogen ions (H⁺, which join water molecules as hydronium ions, H₃O⁺) and negative ions such as chloride (Cl⁻).
Read the full explanation →A wire of copper having length l and area of cross-section A is taken and a current I is flown through it. The power dissipated in the wire is P. If we take an aluminium wire having same dimensions and pass the same current through it, the power dissipated will be
- A.P
- B.< P
- C.> P
- D.2P
Show answer
The power turned into heat in a wire carrying a current I is P = I²R, and the resistance of a wire is R = ρl/A, where ρ is the resistivity of its material.
Read the full explanation →Myopia is also known as :
- A.Far-sightedness
- B.Near-sightedness
- C.Cataract
- D.Presbyopia
Show answer
A person with myopia sees nearby objects clearly but finds distant objects blurred, which is why the defect is called near-sightedness or short-sightedness.
Read the full explanation →