MIDTERM 3 REVIEW SESSION. Dr. Flera Rizatdinova

Transcription

1 MIDTERM 3 REVIEW SESSION Dr. Flera Rizatdinova

2 Summary of Chapter 23 Index of refraction: Angle of reflection equals angle of incidence Plane mirror: image is virtual, upright, and the same size as the object Spherical mirror can be concave or convex Focal length of the mirror:

3 Summary of Chapter 23 Mirror equation: Magnification: Real image: light passes through it Virtual image: light does not pass through 2014 Pearson Education, Inc.

4 Summary of Chapter 23 Law of refraction (Snell s law): Total internal reflection occurs when angle of incidence is greater than critical angle: A converging lens focuses incoming parallel rays to a point 2014 Pearson Education, Inc.

5 Summary of Chapter 23 A diverging lens spreads incoming rays so that they appear to come from a point Power of a lens: Thin lens equation: Magnification: 2014 Pearson Education, Inc.

6 Ch. 23, P.1 Light enters a substance from air at 30.0 to the normal. It continues within the substance at 23.0 to the normal. What is the critical angle for this substance when it is surrounded by air? Solution: sinθ c = n 2 n 1 ; n 2 = n air ; n 1 = n s ; n air sinθ air = n s sinθ s sinθ c = n air n s sinθ c = sin23 sin 30 = 0.78 θ = 51.4 c = sinθ s sinθ air

7 Ch.23 P.2 A concave spherical mirror has a focal length of magnitude 20 cm. An object is placed 30 cm in front of the mirror on the mirror's axis. Where is the image located? Solution: = 1 d o d i f 1 = 1 d o f 1 = d i f d i f d i d o = f d i d i f = 60cm

8 Summary of Chapter 24 Wavelength of light in a medium with index of refraction n: In the double-slit experiment, constructive interference occurs when and destructive interference when Two sources of light are coherent if they have the same frequency and maintain the same phase relationship 2014 Pearson Education, Inc.

9 Summary of Chapter 24 Light bends around obstacles and openings in its path, yielding diffraction patterns Light passing through a narrow slit will produce a central bright maximum of width Interference can occur between reflections from the front and back surfaces of a thin film Light whose electric fields are all in the same plane is called plane polarized The intensity of plane polarized light is reduced after it passes through another polarizer:

10 Ch. 24 P.1 Light of wavelength m passes through two parallel slits and falls on a screen 5 m away. Adjacent bright bands of the interference pattern are 2 cm apart. Find the distance between slits. Solution: d sinθ = mλ d x l = mλ x = lmλ d ; Δx = x 2 x 1 = lλ d Δm; Δm =1 ( adjacent bands) d = lλ Δx = 5m m m = m

11 Ch. 24 P.2 A single slit 1 mm wide is illuminated by 450 nm light. What is the width of the central maximum in the diffraction patter on a screen 6 m away? Solution: sinθ = λ D 1 λ θ = sin = ; D x 1 = l tanθ = 6m tan( ) = m x = 2x 1 = 0.54cm

12 Summary of Chapter 25 Simple magnifier: object at focal point Angular modification: Astronomical telescope: objective and eyepiece; object infinitely far away Magnification: 2014 Pearson Education, Inc.

13 Ch 25, P.1 The focal lengths of the objective lens and the eyepiece of a microscope are 0.50 cm and 2.0 cm, respectively, and their separation adjusted for minimum eyestrain is 6.0 cm. If the microscope is focused on a small object, what is the distance between the object and the objective lens? Answer: 0.57 cm Where the image from objective lens is formed in the microscope? 1 d i + 1 d o = 1 f o ; 1 d 0 = d i = l f e = 6cm 2cm = 4cm 1 0.5cm 1 4cm d o = 0.57cm

14 Ch.25, P2 You have a choice between two lenses of focal lengths f a and f b, where f b = 2f a, to use as the objective lens in building a refracting telescope. If the magnification you obtain using lens a is M a, what will be the magnification when using lens b? A) M b = 2 M a B) M b = 4 M a C) M b = 8 M a D) M b = M a /4 E) M b = M a /2 Answer: A M = f o f e ; Here f o = f a in the first case and f o = f b in the sec ond case

15 Summary of Chapter 27 Planck s hypothesis: molecular oscillation energies are quantized Light can be considered to consist of photons, each of energy Photoelectric effect: incident photons knock electrons out of material An increase in intensity of the light beam results in the larger rate of ejected electrons, but the maximum kinetic energy of electrons is not changed by an increase in intensity If the frequency of the light is increased, the maximum kinetic energy of the electrons increases linearly If the frequency is less that the cutoff frequency, no electrons will be ejected, no matter how great is the intensity of the light.

16 Summary of Chapter 27 Compton effect and pair production also support photon theory Wave-particle duality both light and matter have both wave and particle properties Wavelength of an object with mass: 2014 Pearson Education, Inc.

17 Summary of Chapter 27 Principle of complementarity: both wave and particle properties are necessary for complete understanding Rutherford showed that atom has tiny nucleus Line spectra are explained by electrons having only certain specific orbits Ground state has the lowest energy; the others are called excited states 2014 Pearson Education, Inc.

18 Ch. 27, P1 Light shines through atomic hydrogen gas that was initially in its ground state. You observe that after awhile much of the hydrogen gas has been excited to its n = 5 state. What wavelength of light entering the gas caused this excitation? (c = m/s, h = J s, 1 ev = J) Answer: 95.2 nm E n = 13.6eV n 2 Ground state E 1 = 13.6 ev ΔE = E 5 E 1 = = ev 25 ΔE = hf = hc λ λ = hc = 95.2 nm ΔE

19 Ch. 27, P2 When the surface of a metal is exposed to blue light, electrons are emitted. If the intensity of the blue light is increased, which of the following things will also increase? A) the number of electrons ejected per second B) the maximum kinetic energy of the ejected electrons C) the time lag between the onset of the absorption of light and the ejection of electrons D) the work function of the metal E) all of the above Answer: A