Physics Practice Test: Light and Optics

The angle from the normal is 90° − 25° = 65°, and the angle of reflection equals the angle of incidence. 25° is the angle from the surface, not from the normal.

v = c/n = (3.0 × 10⁸)/1.5 = 2.0 × 10⁸ m/s. 4.5 × 10⁸ m/s multiplies by n, which would make light faster than in a vacuum.

Snell's law: sin θ₂ = sin 30°/1.33 = 0.376, so θ₂ ≈ 22°. Light bends toward the normal when it slows down, so the angle must be smaller than 30°, which rules out 40° and 42°.

sin θ_c = 1/1.50 = 0.667, so θ_c ≈ 41.8°. 48° is the complementary angle, measured from the surface instead of the normal.

1/d_i = 1/10 − 1/30 = 2/30, so d_i = 15 cm, a real image behind the lens. 7.5 cm adds 1/10 and 1/30 instead of subtracting.

Inside the focal length, 1/d_i = 1/10 − 1/5 = −1/10, so d_i = −10 cm: a virtual image with magnification +2. This is how a magnifying glass works.

A plane mirror forms the image as far behind the mirror as you are in front of it, so the image is 2.0 + 2.0 = 4.0 m from you. 2.0 m is the distance from the mirror to the image.

Different wavelengths travel at slightly different speeds in glass, so they bend by different amounts; violet bends the most and red the least. The colors were already in the white light.

Going up in frequency, the order is radio, microwave, infrared, visible, ultraviolet, X-ray, gamma. Infrared lies just below red light in frequency.

f = c/λ = (3.0 × 10⁸)/(7.0 × 10⁻⁷) ≈ 4.3 × 10¹⁴ Hz. 4.3 × 10⁵ Hz forgets that 700 nm is 7.0 × 10⁻⁷ m.