PHYS 1C Lecture Notes - Lecture 15: Real Image, Sign Convention, Virtual Light

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10 May 2018

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Light rays can be diverted by optical systems to fool your eye into thinking an object is somewhere

that it is not

The simplest optical systems are mirrors and lenses

Mirrors and lenses will divert light rays from an object source and create an image

Mirrors use reflection of light to divert the light rays

Lenses use refraction of light to divert the light rays

Images are formed at the point where rays actually intersect or appear to originate from

There are two types of images: real and virtual

A real image is one in which light actually passes through the image point

Real images can be displayed on a screen

A virtual image is one in which the light does not pass through the image point

The light appears to diverge from that point

Virtual images cannot be displayed on screens

The object distance, p, is the distance from the object to the mirror or lens

○

The image distance, q, is the distance from the image to the mirror or lens

○

The lateral magnification, M, of the mirror or lens is the ratio of the image height to the

object height

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To find where an image is formed it is always necessary to follow at least two rays of light as

they reflect from the mirror or refract through the lens

○

For both mirrors and lenses

Mirrors and Lenses

The simplest possible mirror is the flat mirror

We will examine light rays diverging from the top of the object (point p) to geometrically

determine the location of the image

The first light ray starts at point P and moves to point Q

Since this light ray is at 0 degrees to the normal is will just reflect back on itself

A second light ray starts at point P and moves to R

Mirrors

The light ray will reflect off of the mirror according to the Law of Reflection

Tracking back these light rays shows us where the image is

The image is as far behind the mirror as the object is in front (p=q)

The image is unmagnified as the image height is the same as the object height (h=h' and M=1)

The image is upright (same orientation as object)

The image is always virtual

It is not where real light rays converge; only where our eye believes these light rays come from

These dashed imaginary rays are known as virtual light rays

Virtual images are composed of virtual light rays

Your eye tracks back these virtual light rays to form the image

Flat mirrors

There are different types of mirrors

Spherical mirrors have the shape of a segment of a sphere

Concave spherical mirrors have the reflective part on the inner side of the curve

Convex spherical mirrors have the reflective part on the outer side of the curve

Mirrors

The radius of curvature, R, is the radius of the spherical mirror

○

The center of curvature, C, is the center of the spherical mirror

○

Point V is the center of the spherical segment

For concave mirrors we define the following points:

Concave mirrors

(15) Lecture 26A Magnification

Wednesday, May 9, 2018

12:52 PM

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Document Summary

Light rays can be diverted by optical systems to fool your eye into thinking an object is somewhere that it is not. The simplest optical systems are mirrors and lenses. Mirrors and lenses will divert light rays from an object source and create an image. Mirrors use reflection of light to divert the light rays. Lenses use refraction of light to divert the light rays. Images are formed at the point where rays actually intersect or appear to originate from. There are two types of images: real and virtual. A real image is one in which light actually passes through the image point. Real images can be displayed on a screen. A virtual image is one in which the light does not pass through the image point. The light appears to diverge from that point. The object distance, p, is the distance from the object to the mirror or lens.

Related Questions

25) A negative magnification for a mirror means that

A) the image is upright, and the mirror could be either concave or convex.

B) the image is inverted, and the mirror is concave.

C) the image is inverted, and the mirror could be either concave or convex.

D) the image is upright, and the mirror is convex

E) the image is inverted and the mirror is convex.

26) An object is placed in front of a thin lens, Which statements are correct in describing the image formed by the lens? (There could be more than one correct choice.)

A) If the lens is convex, the image must be real.

B) If the image is real, then it is also inverted.

C) If the image is real, then it is also upright.

D) If the lens is convex, the image will never be virtual.

E) If the lens is concave, the image must be virtual.

27) When a beam of light, originally travelling in air, enters a piece of glass having an index of refraction of 3/2, its frequency

A) is unaffected

B) is reduced to 2/3 its original value.

C) increased by a factor of 3/2.

28) The index of refraction of a type of glass is 1.50, and the index of refraction of water is 1.33. If the light enters water from the glass, the angle of refraction will be

A) equal to the angle of incidence.

B) less than the angle of incidence.

C) greater than the angle of incidence.

29) Which of the following terms describe lenses that are thinner at the center than the edges? (there could be more than one correct choice.)

A) concave lenses

B) converging lenses

C) diverging lenses

D) convex lenses

30) You may have seen ambulances on the street with the letters of the word AMBULANCE written on the front of them, in such a way to appear correctly when viewed in your car's rear-view mirror. (See the figure.) How do the letters appear when you look directly at the ambulance (not through the mirror)?

champagnehound445

If a virtual image is formed 9.0 cm along the principal axis from aconvex mirror of focal length â15.0 cm, how far is the object fromthe mirror?

2. A woman looking in a makeup mirror sees her face at twice itsactual size and right-side up. If she is 26.0 cm from the mirror,what is its focal length?

3. Which of the following best describes the image of a concavemirror when the object is at a distance greater than twice thefocal point distance from the mirror?
a. virtual, upright and magnification greater than one
b. real, inverted and magnification less than one
c. virtual, upright and magnification less than one
d. real, inverted and magnification greater than one

4. A convex mirror with focal length of ?18 cm forms an image 12 cmbehind the surface. Where is the object located as measured fromthe surface?

5. A convex mirror with a focal length of ?18 cm forms an image 15cm behind the surface. If the object height is 1.2 cm what is theimage height?

6. An object placed 14 cm from a concave mirror produces a realimage 8.0 cm from the mirror. If the object is now moved to a newposition 18.0 cm from the mirror, where is the new image located asmeasured from the mirror?

7. When the reflection of an object is seen in a concave mirror theimage will:

8. A candle is 40.0 cm in front of a convex spherical mirror ofradius of curvature 70.0 cm. What are the image distance and themagnification, respectively?

9. An object is 16.0 cm from the surface of a spherical Christmastree ornament that is 8.00 cm in diameter. What is themagnification of the image?

10. A solid glass sphere with a radius of 6.00 cm and index ofrefraction of 1.50 has a small coin embedded 3.00 cm from the frontsurface of the sphere. For the viewer looking at the coin throughthe glass, at what distance from the front surface of the glassdoes the coinâs image appear to be located?

11. A glass block, for which n = 1.52, has a blemish located 4.5 cmfrom one surface. At what distance from that surface does the imageof the blemish appear to the outside observer?

12. An object of length 2.00 cm is inside a plastic block withindex of refraction 1.50. If the object is viewed from directlyabove, what is the length of its image?

13. An object is placed at a distance of 25 cm from a thin convexlens along its axis. The lens has a focal length of 10 cm. What arethe values, respectively, of the image distance andmagnification?
14. An object is placed at a distance of 50 cm from a thin lensalong the axis. If a real image forms at a distance of 35 cm fromthe lens, on the opposite side from the object, what is the focallength of the lens?

15. A contact lens is made of plastic with an index of refraction1.50. The lens has an outer radius of curvature of +2.0 cm and aninner radius of curvature of +2.5 cm. What is its focallength?

16. A Youngâs double slit has a slit separation of 2.50 ? 10?5 m onwhich a monochromatic light beam is directed. The resultant brightfringes on a screen 2.00 m from the double slit are separated by2.30 ? 10?2 m. What is the wavelength of this beam? (1 nm = 10?9m)

17. A Youngâs double-slit apparatus is set up so that a screen ispositioned 1.9 m from the double slits, and the spacing between thetwo slits is 0.040 mm. What is the distance between alternatingbright fringes on the screen if the light source has a wavelengthof 630 nm? (1 nm = 10?9 m)

18. The blue tint of a coated camera lens is largely caused by whateffects?

19. What is the minimum thickness of a glycerin film (n = 1.47) onwhich light of wavelength 650 nm shines that results inconstructive interference of the reflected light? Assume the filmis surrounded front and back by air.

20. Light of wavelength 560 nm is incident on a slit of width 0.150mm, and a diffraction pattern is produced on a screen that is 2.00m from the slit. What is the width of the central bright fringe? (1nm = 10?9 m)

21. Light of wavelength 610 nm is incident on a slit of width 0.25mm, and a diffraction pattern is produced on a screen that is 1.5 mfrom the slit. What is the distance of the second dark fringe fromthe center of the bright fringe? (1 nm = 10?9 m)

22. A multiple slit diffraction grating has a slit separation of2.50 ? 10?6 m. Find the wavelength of the monochromatic light thatwill have its second order bright fringe diffracted through anangle of 38.0Â°. (1 nm = 10?9 m)

23. A diffraction grating with 12 000 lines/cm will exhibit thefirst order maximum for light of wavelength 510 nm at what angle?(1 nm = 10?9 m)

24. A beam of unpolarized light in air strikes a flat piece ofglass at an angle of incidence of 58.0Â°. If the reflected beam iscompletely polarized, what is the index of refraction of theglass?

25. A beam of polarized light of intensity I0 passes through asheet of ideal polarizing material. The polarization axis of thebeam and the transmission axis of the sheet differ by 45Â°. What isthe intensity of the emerging light?

26. At what angle is the sun above the horizon if its light isfound to be completely polarized when it is reflected from the topsurface of a slab of glass (n = 1.65)?

PHYS 1C Lecture Notes - Lecture 15: Real Image, Sign Convention, Virtual Light

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