Light And Sound

Question 1

Sound is a wave whose speed cannot be changed by intensity but?

Answer 1

The medium it is traveling in i.e. air

Question 2

For sound what are the two relative characteristics of medium?

Answer 2

1. Bulk Modulus: measure of the medium’s resistance to compression

higher bulk modulus (more the medium resists) → faster sound waves travel

2. Density: With more mass/vol or higher density there is more resistance to motion and lower speeds of sound

Question 3

Sound of speed is faster from highest to lowest

Answer 3

Solid then liquid then gas

Solids have the highest bulk since they’re fully compressed while gas has the lowest bulk

Question 4

Lower density within gases means what speed of sound?

Answer 4

Higher i.e. speed of sound increases as the density decreases (because higher density resists the motion)

Question 5

What’s the equation for speed of sound?

Answer 5

V = Sq. root (Bulk/density)

Question 6

What’s true for all waves?

Answer 6

As waves change medium, the speed will increase or decrease and change wavelengths larger or smaller respectively but frequency will stay same

Question 7

Humans can hear sounds with frequency from 20-20,000 Hz. What are the other sounds called?

Answer 7

Under 20 Hz infrasonic and above 20,000 Hz it is ultrasonic

Question 8

What does frequency depend on?

Answer 8

1. Wave velocity: the faster the wave is moving the higher the frequency will be
2. Wavelength: distance from compression to compression, the larger the wavelength the lower frequency will be

Question 9

What’s equation for frequency and wave speed?

Answer 9

V (wave speed) = frequency * wavelength

Question 10

What’s the equation for Doppler effect?

Answer 10

f’ = f (v +- vD)/(v+- vS)

f’ = perceived frequency
f = actual emitted frequency
v= speed of sound in medium
vD = speed of detector
vS = speed of source

In the eq, if detector moves towards the source, we add and if away we subtract
Meanwhile, if source moves towards the detector, we subtract and if away we add

Question 11

What’s refraction in light waves?

Answer 11

It occurs when light moves from one medium to another

Question 12

What are photons?

Answer 12

Energy through which light travels

Question 13

What does light occur as?

Answer 13

It can occur as a wave or a particle depending on the situation

Question 14

What’s dispersion?

Answer 14

Spreading of light due to differences in the indices of refraction of different colors

Question 15

What’s the point called where lights meet?

Answer 15

Focal point

Question 16

What’s a convex lens?

Answer 16

A lens which has both sides bulging outward. It bend incoming light towards the focal point

Question 17

What’s real image?

Answer 17

It’s inverted produced by a single lens

Question 18

What’s diverging of light?

Answer 18

When light rays spread apart instead of coming to a point

Question 19

What’s concave lens focal point?

Answer 19

It’s where the light is originated from and then gets apart. Notice the focal point doesn’t have all light rays passing through it i.e. that’s why it is called a diverging lens

Question 20

What are virtual images like?

Answer 20

Always upright and not flipped, and they always make the objects in the mirror seem smaller

Question 21

What do concave lens and convex mirror do?

Answer 21

Diverging and always produce virtual image

Question 22

What do convex lens and concave mirror do?

Answer 22

Converging:
Image is real when object distance > focal length
Image is virtual when object distance < focal length

Question 23

What happens in converging system?

Answer 23

The closer the object is the bigger the image
F: Image is closer i.e. larger
2F: image is same size as object
SIR: image is minimized as it’s far.

Note at all points image is real and inverted

Question 24

What are focal length and power for diverging systems?

Answer 24

Negative

Question 25

What’s the equation for power of lens or mirror?

Answer 25

Power = 1/f = 1/image distance + 1/obj. distance

Question 26

At converging system if object is even closer than focal point then it’s BUV?

Answer 26

Image is Bigger, upright, and virtual

Question 27

What’s the mnemonic for diverging system (concave lens and convex mirror)

Answer 27

SUV: Image is smaller, upright, and Virtual

Question 28

What are the important factors for IR spectrum?

Answer 28

Leftmost part from 4000 to 2500 corresponds to bonds containing H atoms. Most useful bonds are OH bond (broad peak) or NH bond (sharp peak) around 3300 cm-1
Note: If N has two hydrogens attached then there will be two peaks

Middle of spectrum from 2500 to 1000 cm-1 contains bonds without Hydrogens such as double or triple bonds (that have higher frequency than single bonds)

Most imp. double bond is C-O or Carbonyl which creates strong, sharp peak at 1700 cm-1

Below 1000, is fingerprint region

Question 29

How does NMR works?

Answer 29

Each peak in proton NMR corresponds to different type of proton. Chemically same protons give a same peak. So two peaks mean two types of protons

Question 30

What does it mean when one peak is larger or one is shorter?

Answer 30

larger peak is made of multiple similar protons while smaller peak is usually representing just one lone proton

Question 31

Things to remember for NMR spectra?

Answer 31

Aldehyde protons peak between 8-10 ppm
Carboxylic Acid proton peak between 10-12 ppm
Aromatic proton peak between 6-8 ppm

Question 32

Splitting in peaks is caused due to?

Answer 32

Due to adjacent protons