PHYSICS FINAL EXAM CH 19-25 Flashcards
(42 cards)
In the equation for speed of a wave, v = 𝑓 𝜆 , name the symbols and units. How are f and related?
- V is the velocity or speed in m/s
- F is the frequency in per sec or /s or Hz
- is the wavelength in meters
- Frequency and wavelength are inversely related
Describe the two types of interference and give examples
- Constructive interference – results in a higher amplitude wave. Ex. Several people yelling the same
thing simultaneously results in a louder sound. - Destructive interference – results in a lower amplitude wave or cancellation. Ex. Noise-cancelling
headphones can reduce/eliminate unwanted sounds
Compare and contrast in-phase and out-of-phase waves
In phase means that the wave forms are similar (crests and troughs are matching) while out of phase
means the exact opposite
Compare and contrast mechanical and electromagnetic waves. Give examples
- Mechanical waves need a material medium for production like waves in a slinky, sound waves, water
waves. - Electromagnetic waves can travel in a vacuum. Examples: radio waves, x-ray, gamma rays, visible
light, UV, infrared, and microwaves
Compare and contrast transverse and longitudinal waves. Give examples and describe particle motion.
- Transverse – all EM waves. Particles move perpendicular to the direction of wave motion.
- Longitudinal – sound waves. Particles move parallel to the direction of wave motion
What is Doppler effect? Give an example
Doppler effect is an apparent change in the frequency due to relative motion between the observer and
the source. One example is the redshift. When stars move away from us, the emitted light waves are
stretched out towards the red end of the electromagnetic spectrum, where light has a longer wavelength
and shorter frequency
How is sound produced?
Sound is produced by any vibrating object.
What factors affect the speed of sound?
The speed of sound is affected by the medium, as well as the density and temperature of the medium
Where will sound speed be the most? the least?
The speed of sound will be fastest in solids, and slowest in air. (The speed of sound is zero in a vacuum
Describe the following properties of waves and give an example for sound.
A. Reflection – bouncing of a wave after hitting a surface. Example: echoes.
B. Refraction – bending of a wave upon hitting the boundary between two substances. Example: Sound bends
upon hitting the boundary between air of different temperatures.
C. Diffraction – bending of a wave around corners or openings/slits. Example. The sound from next door travels
around the corners and is audible.
D. Interference – the superposition of two or more waves. Example: louder sound or sound cancellation
What are different ways of charging objects? Describe each.
- Conduction - via contact between two objects
- Friction –rubbing surfaces against each other
- Induction – bringing a charged object near but not touching another object
What are positive ions? Negative ions?
- Positive ions have more protons or positive charges than electrons
- Negative ions have more electrons or negative charges than protons
Compare and contrast gravitational and electrical forces.
Gravitational forces are always attractive while electric forces can be attractive or repulsive
What is the electric field at the center of a charged spherical conductor?
zero
What happens to the current in a circuit when you add a second light bulb? Compare for series and parallel
circuits.
- In a series circuit, adding a second light bulb corresponds to an increase in the total resistance for the
circuit. From Ohm’s law, this would then decrease the total current supplied to the circuit. - In a parallel circuit, adding a second light bulb corresponds to a decrease in the total resistance for the
circuit. From Ohm’s law, this would then increase the total current supplied to the circuit.
Describe Ohm’s law
Ohm’s law is Voltage = Current x Resistance. The current is equal to the ratio of the voltage to the
resistance
What are examples of magnetic and non-magnetic materials?
- Magnetic – iron, nickel, cobalt, steel
- Non-magnetic – paper, wood, aluminum, gold
How can you remove magnetism/magnetic field?
- For a magnet, apply pressure or heat until there is no longer a magnetic domain.
- For an electromagnet, remove the source of the current
What is meant by a neutral atom?
It has a total charge of zero
What determines the direction of the electric field? Describe the electric field for a positive and a negative
charge.
The direction of the electric field is in the same direction as the force on a small test charge. It is
radially outwards for a positive point charge and radially inwards for a negative point charge
What is Coulomb’s law? Identify the variables and units involved.
𝐹 = 𝑘 𝑞1𝑞2
𝑟2 where F is the force, q1 and q2 are the charges, and r is the distance between q1 and q2
What happens to the force between charges if the distance is doubled? Halved?
The force between charges will reduced to ¼ the original if the distance is doubled.
- The force between charges will quadruple when the distance is halved.
Compare and contrast conductors and insulators. Give examples.
Conductors – easily allow electron flow. Examples: copper, gold
- Insulators – do not easily allow electron flow. Examples: wood, plastic
Which will accelerate more for the same force, a proton, or an electron? Why?
The electron has a smaller mass compared to the proton so following Newton’s second law,
∑ 𝐹 = 𝑚 𝑎, a smaller mass will have more acceleration
