(a) A 2.20 cm high insect is 1.23 m from a 140 mm focal-length lens. What is the

Question

(a) A 2.20 cm high insect is 1.23 m from a 140 mm focal-length lens. What is the image distance? (mm)

(b) How high is the image? (cm)

(c) What type is it? (Select all that apply.)

a. The image is real

b. The image is in front of the lens.

c. The image is upright.

d. The image is inverted.

e. The image is virtual.

f. The image is behind the lens.

(d) What if f = -140 mm? What is the image distance? (mm)

(e) How high is the image? (cm)

(f) What type is it? (select all that apply)

a. The image is real.

b. The image is virtual.

c. The image is inverted.

d. The image is in front of the lens.

e. The image is upright.

f. The image is behind the lens.

Explanation / Answer

a) Use equation,

1/f=1/do+1/di

1/0.140=1/1.23+1/di        => di=0.18m = 18cm

b)M=hi/ho=-di/do=

hi=(-di/do)*ho = (-0.18/1.23)*0.022 = 0.0032 = 3.2 mm

c) Plus sign confirms that image is real , inverted and behind the lens.

d) Use equation,

1/f=1/do+1/di

1/-0.140=1/1.23+1/di        => di=-0.00126m =-126mm

e)M=hi/ho=-di/do=

hi=(-di/do)*ho = (-(-0.00126)/1.23)*0.022 = 22.5m

f) Plus sign confirms that image is real , inverted and behind the lens.

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