PHYSICS FINAL EXAM REVIEW

1. PHYSICS FINAL EXAM REVIEW Answer Key! Text me if you have any questions! (Especially 1st 3rd and 6th period )

2. 1. B Frequency is the number of waves/vibrations/pulses/oscillations that occur in one second. Frequency is measured in Hertz. Period is the number of seconds per wave, or 1/f  Amplitude Wavelength 

3. 2. B, 12. A • Refraction is when the light bends as it changes the medium it’s traveling through (air to glass, glass to water, water to air, etc)

4. 3. A, 11. C • Refraction and Diffraction are BOTH about waves bending, but for different reasons. Diffraction is when they spread out around the edge of a wall, or as they go through a hole in a wall:

5. 4. D • Remember, in physics, “reflection” doesn’t mean what you see in the mirror (that’s an image). Reflection is when waves bounce off of an object. An echo happens when sound waves reflect off of a barrier and come back to your ear.

6. 5. B Sound waves are the most common example of a longitudinal wave. Longitudinal waves happen when the particles of the medium move back in forth in the same direction as the wave is moving:

7. 6. B, 7. C • As it passes you, the apparent frequency suddenly drops, resulting in a low pitch: • http://www.physicsclassroom.com/Class/sound/u11l3b.cfm

8. 8. D • High frequency = high pitch • Low frequency = low pitch • http://plasticity.szynalski.com/tone-generator.htm <-- This website lets you pick a frequency and will play the sound so hear the difference between a high frequency and a low frequency (only works in firefox) • (The LOUDNESS depends on the amplitude.)

9. 9. A • Electromagnetic waves do not require a medium to travel through. They are transverse waves.

10. 10. B • Transparent = lets all light through (window) • Opaque = lets no light through (wall) • Translucent = lets some light through (frosted window) • Luminous = gives off light (light bulb)

11. 13. D

12. 14. A • Remember the electric field hockey simulation: http://phet.colorado.edu/en/simulation/electric-hockey • To change the force on the “puck” you can change the charge of the puck OR change the size of the field.

13. 15. A • Ohm’s Law says I = V/R • I = Current (measured in amps) - Current is the amount of charge flowing • V= Voltage (measured in volts)- Voltage is the energy per charge • R = Resistance (measured in ohms Ω)- Resistance resists or slows down the flow of charge. • According to the equation, if V increases, then so does I. If R decreases, I increases.

14. 16. D • Ammeters measure amps (units of current) • Voltmeters measure volts (units of voltage) • Ohmmeters measure ohms (units of resistance)

15. 17. C • One path only:

16. 18.A RT = R+R+R+R = 4R

17. 19. D • Three paths:

18. 20. B • A circuit breaker uses an electromagnet to literally “break the circuit” if there is a dangerous level of current. (This was one of our uses of electromagnets – remember the Brainpop video we watched on electromagnets – or rewatch it. Text me for the password) • A fuse does the same thing with a melting wire and has to replaced each time, while a circuit breaker can be reset.

19. 21. B • Moving charges create a magnetic field – an electromagnet. • We can increase the strength by: • -Increasing the current (usually by increasing the voltage) • - Wrapping the wire into coils – more coils = stronger magnetic field • - wrapping the wire around an iron core (or any other ferromagnetic material – ferromagnetic = attracted to magnets) REMEMBER: Moving charges (current) create a magnetic field AND Moving/changing magnetic fields create a current.

20. 22. TRUE To measure the correct current, you don’t want the current to change when you hook up the ammeter. If you connect it in series, the current will stay the same in the resistor you are measuring. If you connect it in parallel the current will change in the resistor you are measuring because current is split up between the components in a parallel circuit.

21. 23. TRUE In the equation for a parallel circuit, RT will always be smaller than any of the individual resistances in the circuit. (Try it if your not sure!) AND – the more resistors you add to the circuit in parallel, the SMALLER the total resistance will be! It seems weird, but we measured it ourselves in the lab and got the same results!

22. 24. TRUE • Frequency is waves/second • Period is seconds/wave • f= 1/T (T = period) • T = 1/f

23. 25. FALSE • Frequency is measured in hertz • Wavelength (and amplitude)are measured in METERS

24. 26. TRUE • v = wavespeed • λ = wavelength • f = frequency • v = λf • Also – you need to be able to rearrange this: • λ = v/f • f = v/λ

25. 27. TRUE • F = ILB • F = magnetic force (N) • I = current (amps) • L = length of wire in field (m) • B = magnetic field strength (Teslas T) • Magnetic field must be perpendicular to the current!

26. 28. FALSE Telescopes make faint objects look brighter (and bigger, but mostly brighter. Also – pretty much all of them that aren‘t toys use a mirror, not a lens. Only the eyepiece has lenses these days. ) Microscopes make small things look bigger. You’re seeing a virtual image of a real image! Concave Convex

27. 29. TRUE • But what about the ocean?? Or a swimming pool?? Liquids only transmit transverse waves on the very surface. Think about it, can the whole entire swimming pool from top to bottom move like this?

28. 30. FALSE • Nope, this is describing a transverse wave. In a transverse wave, the particles of the medium move perpendicular to the direction of wave motion. Watch one of the dots – the dots are moving up and down, while the wave is moving left to right:

29. 31. FALSE • The magnetic field must be perpendicular (right angle) to the current.

30. 32. TRUE • EMF = BLv • EMF = “electromotive force” – voltage caused by electromagnetic induction (volts) • B = magnetic field strength • v = velocity of the wire moving through the field REMEMBER: Moving charges (current) create a magnetic field AND Moving/changing magnetic fields create a current.

31. 33. FALSE • An electric generator generates electricity – it turns mechanical energy into electric energy. • An electric generator uses a spinning electromagnet (mechanical energy) to create a current (electric energy)

32. 34. TRUE • An electric generator uses a spinning electromagnet (mechanical energy) to create a current (electric energy) • An electric motor uses current flowing through a wire (electric energy) that then begins to spin (mechanical energy) due to a force from a magnetic field.

33. 35. FALSE • A step-up transformer “steps up”, or increases the voltage. So the secondary voltage would be higher than the primary voltage. • http://hyperphysics.phy-astr.gsu.edu/hbase/magnetic/transf.html

34. 36. TRUE • EMF = -nΔBA/Δt • The faster the current changes, the faster the magnetic field induced by the current (B) will change, that is Δt will decrease, and EMF will increase. • n = number of coils of wire • ΔB = change in magnetic field strength • A = area of coil • Δt = change in time during change of field strength

35. 37. FALSE • A red dress REFLECTS red light and ABSORBS other colors. • A red dress illuminated only by green light will ABSORB the green light and REFLECT nothing – it will look black.

36. 38. B • v = 5600 m/s • λ = ? • f = 2240 Hz • λ = v/f • λ = 5600/2240 m • λ = 2.5 m

37. 39. B • Period is the amount of time it takes for one pulse/wave/vibration/oscillation • If it takes 4 seconds for 8 pulses, then each pulse takes 0.5 seconds. • (T = seconds/wave = 4/8 = 0.5 seconds)

38. 40. D • Frequency is the number of waves/vibrations/pulses/oscillations that occur in one second. • If there are 8 pulses in 4 seconds then there are 2 pulses every second. • Alternate: f = waves/sec = 8/4 = 2 Hz • Alternate: T = 0.5s (from 39) and f = 1/T = 1/0.5 = 2 Hz

39. 41. D • Speed = distance/time; distance = speed*time • distance sound travels = speed of sound* time • Speed of sound = 344 m/s • Time = 2.5 • Distance sound travels = 860 m – this is the distance to the iceberg and back again. • The iceberg is 860/2 = 430m away

40. 42. C • λ = ? • f = 5.0 X 1014 Hz • v = 3 X 108 m/s • λ = v/f • λ = (3 X 108m/s)/(5.0 X 1014Hz) • λ = 6 X 10-7m

41. 43. A

42. 44. A • Coulomb’s Law: • F = kq1q2/d2 • F = Force (N) • k = Coulomb’s Constant = 9.0 x 109 N • m2 / C2 • q = electric charge (C) • d = distance (m) • q1= 3.9X10-5 C • q2= 3.2X10-5 C • d=0.033 m • F = ? • F = kq1q2/d2 • F=(9X109)(3.9X10-5)(3.2X10-5) • 0.0332 • F = 1X104 N

43. 45. B • P= IV • P= Power (Watts) • I = Current (Amps) • V = (Volts) • P = ? • V = 120 V • I = 1.25 A • P = IV • P = 1.25*120 Watts • P = 150 Watts

44. 46. B • R1 = 9.0 Ω • R2 = 3.0 Ω • VT = 6.0 V • RT (series) = R1 + R2 • RT= 9.0 Ω+ 3.0Ω • RT = 12 Ω

45. 47. C • R1 = 18 Ω • R2 = 25 Ω • 1/RT (parallel)= 1/R1+ 1/R2 • 1/RT= (1/18 Ω) + (1/25 Ω) • 1/RT = 0.1 • RT = 1/0.1 • RT = 10 Ω

46. 48. A • L= 0.25m • I = 1.25 A • B = 0.32 T • F= ? • F= ILB • F= (1.25)(0.25)(0.32)N • F= 0.10 N

47. 49. C • L=33.0m • B= (5.3 X 10-4) T • v = 16.0 m/s • EMF = ? • EMF = BLv • EMF = (5.3 X 10-4)(33.0)(16.0) V • EMF = 0.28 V

48. 50. D • Transformers: • Np/Ns = Vp/Vs = Is/Ip • N = number of turns • V= voltage • I = Current • p = primary • s= secondary • Don’t forget, for current, it’s secondary over primary! • Vp = 220000 V • Vs = 440 V • Np/Ns = ? • Np/Ns = Vp/Vs • Np/Ns = 220000/440 • Np/Ns = 500

49. 51. C • I don’t really have anything to say about this, it’s just a definition, and there’s nothing else that really goes with it. • I guess it helps to know that even though light is a wave, you can also think of it as these little packets (or ping pong balls ) called photons bouncing around. • A light ray in a ray diagram is tracing the path of a single photon as it travels – bouncing off of mirrors and bending as it goes through a lens. • I really wish I had thought of this explanation of light rays before Friday night. Many thanks to Marisol for helping me think of a different way to describe them!

50. 51. C • If you are reading this, write the word batman on the subject line of your scantron during the exam for two points of extra credit. • If you tell people who haven’t read this review about the batman points, then the game is ruined, and you’re no fun. And if I found out that word has spread, then no one gets points. • If someone asks you why you’re writing down “batman” you can tell them about this secret slide, but that I said to write down your favorite superhero, and that if I saw any two that were the same, I would assume people were just copying it and no one would get any points. • I need to go to sleep. I hope you have enjoyed the secret batman extra credit game review slide.