Chapter 10: Lens and Mirror Signs

Question 1

When o of the mirror equation is positive and negative:

Answer 1

Positive: object is in front of mirror (real image)

Negative: object is behind mirror (virtual image)

Question 2

When i of the mirror equation is positive and negative:

Answer 2

Positive: image is in front of mirror (real image)

Negative: image is behind mirror (virtual image)

Question 3

When r of the mirror equation is positive and negative:

Answer 3

Positive: concave mirrors

Negative: convex mirrors

Question 4

When f of the mirror equation is positive and negative:

Answer 4

Positive: concave mirrors

Negative: convex mirrors

Question 5

When m of the mirror and lens equations is positive and negative:

Answer 5

Positive: image is upright (erect)

Negative: image is inverted

Question 6

When absolute value of m of the mirror and lens equations is greater than 1 and les than 1:

Answer 6

Greater than 1: enlarged

Less than 1: reduced

Equal to 1: same size

Question 7

When o of the lens equation is positive and negative:

Answer 7

Positive: object on side of lens light is coming from (virtual side)

Negative: object on side of lens light is going to (real side)

Question 8

When i of the lens equation is positive and negative:

Answer 8

Positive: image on side of lens light is going to (real side)

Negative: image on side of lens light is coming from (virtual side)

Question 9

When r of the lens equation is positive and negative:

Answer 9

Positive: when on real side (convex surface as seen from side light is coming from)

Negative: when on virtual side (cocave surface as seen from side light is coming from)

Question 10

When f of the lens equation is positive and negative:

Answer 10

Positive: converging lens

Negative: diverging lens

Question 11

Law of Reflection equation:

Answer 11

θ₁ = θ₂

where θ₁ is the incident angle and θ₂ is the reflected angle

the angles are always measured from normal (a line perpendicular to the surface of the medium)

Question 12

Equation to determine the object or image distance from a mirror, focal length, or radius of curvature:

Answer 12

¹/_o + ¹/_i = ¹/_f = ²/_r

where o is the distance of the object from the mirror, i is the distance of the image from the mirror, f is the distance from the focal point to the mirror (focal length), and r is the distance between the center of curvature and the mirror (for spherical mirrors)

units = m^-1

Question 13

Equation to find the magnification of an image for both mirrors and lenses:

Answer 13

m = - ⁱ/_o

where o is the distance of the object from the mirror and i is the distance of the image from the mirror or lens

if the absolute value of m is less than 1, the image is reduced

if the absolute value of m is greater than 1, the object is enlarged

Question 14

Equation to determine the index of refraction:

Answer 14

n = ^c/_v

where c is the speed of light in a vacuum (3.8 X 10⁸), v is the speed of light in the given medium, and n is the index of refraction

Question 15

Equation to find the degree of refraction of a light ray upon entering a new medium:

Answer 15

n₁sinθ₁ = n₂sinθ₂

theta is always measured with respect to the perpendicular to the boundary

Question 16

Equation to determine the critical angle:

Answer 16

derived from Snell’s Law

sinθ_c = n₂ / n₁

Question 17

Equation to determine object distance (o), image distance (i), focal length (f), and magnification (m) for lenses:

Answer 17

¹/_o + ¹/_i = ¹/_f

m = ^-i/_o

Question 18

Equation to determine the focal length in lenses where thickness cannot be ignored:

Answer 18

¹/_f = (n-1)(¹/r₁ - ¹/r₂)

where n is the index of refraction of the lens material, r₁ is the radius of the curvature of the first lens surface, and r₂ is the radius of curvature of the second lens surface