Reflection of Light: Mirrors — Practice Quiz

A Physics cheat sheet for Reflection of Light: Mirrors — every key formula with its symbols defined — plus a medium-level practice quiz to test recall.

Formulas & key concepts

Law of Reflection: The angle of incidence \(\theta_i\) equals the angle of reflection \(\theta_r\).

$$\theta_i = \theta_r$$

Focal Length (Concave Mirror): Focal length \(f\) is half the radius of curvature \(R\).

$$f = \frac{R}{2}$$

Focal Length (Convex Mirror): Focal length \(f\) is negative half the radius of curvature \(R\).

$$f = -\frac{R}{2}$$

Mirror Equation: Relates object distance \(d_o\), image distance \(d_i\), and focal length \(f\).

$$\frac{1}{d_o} + \frac{1}{d_i} = \frac{1}{f}$$

Magnification Equation: Relates magnification \(m\), image height \(h_i\), object height \(h_o\), and distances.

$$m = \frac{h_i}{h_o} = -\frac{d_i}{d_o}$$

Practice quiz

  1. If a light ray strikes a plane mirror at an angle of incidence of $35^\circ$, what is the angle of reflection?

    • $35^\circ$
    • $55^\circ$
    • $70^\circ$
    • $17.5^\circ$

    Answer: $35^\circ$

  2. A concave mirror has a radius of curvature of $40 \text{ cm}$. What is its focal length?

    • $20 \text{ cm}$
    • $-20 \text{ cm}$
    • $40 \text{ cm}$
    • $-40 \text{ cm}$

    Answer: $20 \text{ cm}$

  3. A convex mirror has a radius of curvature of $60 \text{ cm}$. What is its focal length?

    • $30 \text{ cm}$
    • $-30 \text{ cm}$
    • $60 \text{ cm}$
    • $-60 \text{ cm}$

    Answer: $-30 \text{ cm}$

  4. An object is placed $30 \text{ cm}$ in front of a concave mirror with a focal length of $10 \text{ cm}$. Where is the image formed?

    • $15 \text{ cm}$
    • $7.5 \text{ cm}$
    • $-15 \text{ cm}$
    • $-7.5 \text{ cm}$

    Answer: $15 \text{ cm}$

  5. An object is placed $20 \text{ cm}$ in front of a convex mirror with a focal length of $10 \text{ cm}$. Where is the image formed?

    • $6.67 \text{ cm}$
    • $-6.67 \text{ cm}$
    • $20 \text{ cm}$
    • $-20 \text{ cm}$

    Answer: $-6.67 \text{ cm}$

  6. An object $5 \text{ cm}$ tall is placed in front of a mirror. Its image is $15 \text{ cm}$ tall and inverted. What is the magnification?

    • $3$
    • $-3$
    • $0.33$
    • $-0.33$

    Answer: $-3$

  7. A $2 \text{ cm}$ tall object is placed $15 \text{ cm}$ in front of a concave mirror with a focal length of $10 \text{ cm}$. What is the height of the image?

    • $4 \text{ cm}$
    • $-4 \text{ cm}$
    • $2 \text{ cm}$
    • $-2 \text{ cm}$

    Answer: $-4 \text{ cm}$

  8. When an object is placed between the focal point and the center of curvature of a concave mirror, the image formed is:

    • Real, inverted, and magnified
    • Virtual, upright, and magnified
    • Real, inverted, and diminished
    • Virtual, upright, and diminished

    Answer: Real, inverted, and magnified

  9. Which of the following statements is true for a convex mirror?

    • It always forms real images
    • Its focal length is always positive
    • It always forms virtual, upright, and diminished images
    • It can form both real and virtual images

    Answer: It always forms virtual, upright, and diminished images

  10. An object is placed $25 \text{ cm}$ from a mirror. A virtual image is formed $10 \text{ cm}$ behind the mirror. What is the focal length of the mirror?

    • $16.67 \text{ cm}$
    • $-16.67 \text{ cm}$
    • $7.14 \text{ cm}$
    • $-7.14 \text{ cm}$

    Answer: $-16.67 \text{ cm}$

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