# Optics: Twelve problems on different properties of light.

1. A dentist uses a mirror to examine a tooth that is 1.00 cm in front of the mirror. The image of the tooth is formed 10.0 cm behind the mirror. Determine (a) the mirror's radius of curvature and (b) the magnification of the image.

2. An object is placed 40.0 cm from a concave mirror of radius 20.0 cm. (a) Find the location of the image. (b) What is the magnification of the mirror? Is the image real or virtual? Is the image real or virtual? Is the image upright or inverted?

3. A concave makeup mirror is designed so that a person 25 cm in front of it sees an upright image magnified by a factor of two. What is the radius of curvature of the mirror?

4. A man standing 1.52 m in front of a shaving mirror produces an inverted image 18.0 cm in front of it. How close to the mirror should he stand if he wants to form an upright image of his chin that is twice the chin's actual size?

5. A converging lens has a focal length of 10.0 cm. Locate the images for object distances of (a) 20.0 cm, (b) 10.0 cm, and (c) 5.00 cm, if they exist. For each case, state whether the image is real or virtual, upright or inverted, and find the magnification.

6. A diverging lens has a focal length of 20.0 cm. Locate the images for object distances of (a) 40.0 cm, (b) 20.0 cm, and (c) 10.0 cm. For each case, state whether the image is real or virtual and upright or inverted, and find the magnification.

7. A laser beam is incident on two slits with a separation of 0.200 mm, and a screen is placed 5.00 m from the slits. If the bright interference fringes on the screen are separated by 1.58 cm, what is the wavelength of the laser light?

8. Light of wavelength 5.30 x 10^2 nm illuminates a pair of slits separated by 0.300 mm. If screen is placed 2.00 m from the slits, determine the distance between the first and second dark fringes.

9. A Young's double-slit interference experiment is performed with blue-green argon laser light. The separation between the slits is 0.500 mm, and the screen is located 3.30 m from the slits. The first bright fringe is located 3.40 mm from the center of the interference pattern. What is the wavelength of argon laser light?

10. A light source emits two major spectral lines: an orange line of wavelength 610 nm and a blue-green line of wavelength 480 nm. If the spectrum is resolved by a diffraction grating having 5000 lines/cm and viewed on a screen 2.00 m from the grating, what is the distance (in centimeters) between the two spectral lines in the second-order spectrum?

11. Light from an argon laser strikes a diffraction grating that has 5310 grooves per centimeter. The central and first-order principal maxima are separated by 0.488 m on a wall 1.72 m from the grating. Determine the wavelength of the laser light.

12. Does your bathroom mirror show you older or younger than your actual age? Compute an order-of-magnitude estimate for the age of difference.

#### Solution Preview

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12 Physics Questions

Redding:

The object distance q the image distance p and the focal length for a mirror is related as

The sign convention is

1. All distances are measured from the optical center of the lens or pole (vertex) of the mirror.

2. The distances measured in the direction of the incident rays are taken positive and in the direction opposite to that of incident rays are taken negative.

3. The lengths (object or image) measured above the principle axis are taken positive and in lower half plane are negative.

4. The focal length of converging lens is positive.

As the focus point F of the concave mirror is in front of the mirror its focal length OF = f will be negative.

As the rays are coming from a real source the object distance will be opposite to the incident ray and thus should be taken negative.

1. A dentist uses a mirror to examine a tooth that is 1.00 cm in front of the mirror. The image of the tooth is formed 10.0 cm behind the mirror. Determine (a) the mirror's radius of curvature and (b) the magnification of the image.

Here the object distance is q = - 1 cm

The image is behind the mirror thus p = + 10 cm

(a) Thus the focal length of the mirror is given by

Or

Or

Gives f = - 10/9 = - 1.11 cm

As the focal length of a mirror is half of the radius of curvature, we get radius of curvature of the mirror as

R = 2f = 2*(-1.11) = - 2.22 cm.

Thus the radius of curvature of the mirror is 2.22 cm.

(The negative sing shows that it is a concave mirror)

(b) The magnification m of an image for a mirror is given by

Hence substituting the values we get

(The positive sign is due to the image is erect.)

2. An object is placed 40.0 cm from a concave mirror of radius 20.0 cm. (a) Find the location of the image. ...

#### Solution Summary

Twelve problems related to reflection, reflection, interference, dispersion are solved and explained.