Waves

Question 1

Mechanical waves
(11 points total)
(4 points each wave)

Answer 1

Transverse waves
Perpendicular to the direction of propagation.
Solids and surfaces of liquids.
Have crest and troughs.
Water waves, S-seismic waves.
Longitudinal waves
Parallel to the direction of propagation.
Have compressions and rare-factions.
Sound waves and p-seismic waves.
Travel in fluids.
In both of these waves, only energy travels.

Question 2

In which medium are waves faster

Answer 2

Solids- As the particles can come back to their original position faster after they vibrate .

Question 2

Amplitude

Answer 2

It is the distance form the equilibrium line to the maximum point of the wave.
It determines how loud the sound is.
loudness ∝ a^2

Question 3

Wavespeed formula

Answer 3

wavespeed= lamda/time period[t]

v=λ*(1/t)
1/t=frequancy
v= λf

Question 4

Reflection laws

Answer 4

1. The incident ray, reflected ray and normal, from the point of incident lie on the same plane.
2. ∠i=∠r

Question 5

Reflection types

Answer 5

If a ray retraces its path(it is parallel to the normal), the angle between normal and rays is 0
Regular reflection- all waves have same ∠i and ∠r.
Diffused reflection- ∠i and ∠r are same for each individual ray but not same for all the rays. Happens on a rough surface.

Question 6

2 mirrors are kept at an angle. Formula

Answer 6

360/∠ between the mirrors.

Question 7

Refraction

Answer 7

Bending of light as it travels to a medium with different density.
As it goes to an optically denser medium from an optically rarer on, the speed decreases and so the ray moves closer to the normal.

It it moves from an optically denser to and optically rarer medium, the speed increases bending away from the normal.
The angle of deviation is the change in the angle compared to angle on incidence.

Question 8

Refraction laws

Answer 8

1. The incident ray, refracted ray and normal, from the point of incident lie on the same plane.
2. The speed of light in vacuum and the speed of light in air bare a constant ratio called reflective index[n]
   n=sin i/sin r
   n= c(vacuum)/v(medium)
   n1 sin i = n2 sin r
   n=1/sin c

Question 9

Can rays which are not parallel to the normal go un-deviated in refraction

Answer 9

Yes, due to physical changed done in density.

Question 10

Critical angle

Answer 10

The angle of incidence at which the angle of refraction is 90 degrees.

Question 11

Total internal reflection

Answer 11

1. The ∠i >∠ I[c]
2. The ray is either in a denser medium or travelling to a denser medium.

Question 12

When wave is parallel to the normal

Answer 12

The ray goes undeviated

Question 13

Emerging angle

Answer 13

∠i=∠e

Question 14

Lens labelling

Answer 14

Principal axis
Radius of curvature
Radius of aperture
Focal length
Focal point

Question 15

Convex lens

Answer 15

Magnification can be >1, <1, 1.
+ve focal length, -ve object distance, +ve image distance (except in magnifying lens)

Question 16

Magnification

Answer 16

Image distance/object distance

Question 17

Concave lens

Answer 17

Magnification is always <1.
-ve focal length, -ve object distance, -ve image distance

Question 18

Converging power

Answer 18

1/F(m)=Power
p is inversly propotional to focal length

Question 19

Lateral dispalcement

Answer 19

lateral displacement ∝ distance
lateral displacement ∝ ∠i
The displacement happening in glass blocks

Question 20

Prisms

Answer 20

Angular displacement after which the light bends towards the base.
Dispersion
(splitting of light takes place)
The red light bends the least and violet bends the most so violet is closest to the base.
Bending ∝ 1/wavelength

Question 21

Monochromatic light

Answer 21

Visible beam of light with a single frequancy

Question 22

3 types of beam of light

Answer 22

converging, diverging, parallel.

Question 23

Deflects of eye

Answer 23

Hypermetropia- Long sidedness
You can see objects at a distance but not the ones closer. This happens as the ray of light falls way ahead of the retina. Fixed using converging lens.

Myopia- Short-sidedness
When you can see objects nearer to you but not the ones far away. Happens when the image is formed behind the retina and cant reach the retina.
Can be fixed by using diverging lens (concave lens)

Question 24

when is a virtual image formed.

Answer 24

when diverging rays are extrapolated backwards and does not form a visible projection on a screen

Question 25

Electromagnetic spectrum

Answer 25

In increasing frquancy and decreasing wavelength Max wavelength/least freq Radio waves, Microwaves, Infrared waves, Visible light(ROYGBIV), Ultraviolet, X-rays, Gamma rays All are transverse in nature All travel at the speed of light All travel in vacuum. Gamma rays have highest energy.

Question 26

Uses of waves (Radio, micro, Infrared)

Answer 26

Radio waves- Communication as they can pass through walls but the signals might be weak. Astronomy, radio frequency identification. Bluetooth is also used as they can pass through walls. Microwaves- Mobile phones and Wi-fi as they can pass through walls. Used in satellites (geostationary and low orbit artificial satellites). They require a short aerial for transmission and reception Infrared- Short distance communication such as Tv remote signals, Intruder alarms, Thermal imaging, optical fibers, electric grills. Can transfer data fast. optical fibres (visible light or infrared) are used for cable television and high-speed broadband because glass is transparent to visible light and some infrared; visible light and short wavelength infrared can carry high rates of data

Question 27

Uses of waves(Ultraviolet, x-rays, gamma rays)

Answer 27

UV rays- Vitamin d, sterilize water, Security marking, Detecting fake bank notes. X-rays- Observing bones, detecting metal in luggage, security scans. Gamma rays- Sterilize food and instruments, detect cancer cells and kill them.

Question 28

Harms of electromagnetic radiation

Answer 28

X-rays and gamma rays- Highly ionizing and so can penetrate into your skin causing cancer. Infrared- Can cause extensive causing burns and damage. UV rays- Can cause damage in the cells and skin cancer. Microwave- Can destroy cells and cause internal heating.

Question 29

Types of signals

Answer 29

Analogue- continuous If it looses energy, it is very hard to get it back digital- fixed values. Higher rate of transmission Higher range of transmission( as it is easy to regenerate these)

Question 30

Sound(5 points)

Answer 30

Longitudinal and mechanical waves. In air the speed is 330-350m/s Can change pressure. The graph for pressure looks like a transverse wave diagram where the crest is the compression and trough is the rare faction. Audible range is 20H-20Khz.

Question 31

How does vibration create sound (5 points)

Answer 31

When object vibrates the sound travels. The object causes the surrounding air particles to vibrate. When sound reaches your ear, your ear drum vibrates and so your brain interprets it as sound. Sound needs a medium to travel.

Question 32

How to measure sound

Answer 32

Apparatus: A gun which creates sound and light, 2 people, 1 stopwatch. Person 1 shoots the gun and person 2 starts the stop watch as soon as they see the light. Then person 2 stops as soon as they hear the sound. Sound can be calculated.

Question 33

Echo

Answer 33

The reflecting back of sound. 2d/t

Question 34

Diffraction

Answer 34

Spreading of light when it hits obstacles. More gap ∝ 1/ diffraction more wavelength ∝ diffraction If the gap is less, the waves are circular.

Question 35

Wave motion

Answer 35

Wave motion is the transfer of energy from one point to another through a medium, without the actual movement of the medium itself

Question 36

A sound and light coming in the same room. The sound diffracts more. What could be the reason.

Answer 36

The sound could have a greater wavelength.

Question 37

Diffraction through an edge

Answer 37

When there is only one side of the obstacle or one edge only that end reflects. The more the wavelength, the more diffraction will happen.

Question 38

How to draw a wave refracting into deep water

Answer 38

RNAR Ray of incidence, Normal (90 degree), Angle i, Refracted ray Steps 1. Draw a complete ray of incidence till the boundary. 2. Draw normal perpendicular to the normal. 3. Mark angle i. 4. Draw where the refracted ray would be.(In this case since the ray speed up it will bend away from the normal. ) 5. Draw the wavefronts perpendicular to the refracted ray.

Question 39

Ripple tank

Answer 39

A shallow tray of water. A lamp on the top with white paper at the bottom. To measure wavelength:- Take a picture of the waves and then measure the distance between 10 of them (for accuracy) and divide by 10 to get the value of 1 wavelength. Frequency Take a stopwatch Start it and start counting the number of waves passing by a particular point in 10 seconds( for accuracy). Then divide the number of waves by 10. Waves speed can be found using w=λf

Question 40

Internal reflection

Answer 40

Happens when light is in the dense medium When light escapes the dense medium some of it reflects back which is internal reflection.

Question 41

examples of total internal reflection

Answer 41

Optical fibers: A light signal is sent to one end. The signal hits the inner surface at an angle higher than the critical angle. This causes total internal reflection. Advantages: Long distance data transmission as no power loss. Immune to electrical interference. Cheaper Better than copper wires. It can break if bent too much. Other uses: Periscopes Diamond sparkle

Question 42

Ultra sound

Answer 42

Travels through material and reflects if hit by any object or any flaws is noticed.(stops when meets a boundary between different subjects).

Question 43

Uses of ultrasound

Answer 43

1. Non-destructive testing:- To detect internal flaws in an object. U-sound is sent into the material. It reflects back if flaws found. A detector receives these signals and determines the distance of the flaw using echo. No damage and is safe, finds invisible cracks. 2. Medical use To create images of soft tissues and unborn babies. 1. U-sound pulse is sent in. 2. It reflects off when hits something. 3. A live image of soft tissues is created. 4. Fetus and blood flow (using doppler u-sound) can be seen. Painless, no ionization, less harmful, good for repetitive use. Less detail since wavelength is shorter. 3. SONAR Emit u pulse When hit by something in the ocean it reflects back sound. Detected by a detector. Converted into distance to calculate the depth of the ocean, mapping sea floor, objects under ocean and depth of shoal of fish.