A disturbance in a medium that transmits energy without a net movement of the medium or particles is a wave. A wave usually involves a periodic, repetitive movement. A wave may take the form of pressure variation, elastic deformation, electric or magnetic concentration, and temperature.
The distance between an identical part of the wave is called wavelength. The maximum displacement from the neutral position is called amplitude. The position of a particular point in the medium is called displacement; as the wave passes, it moves.
Types of Waves:
- Transverse Waves
- Longitudinal Wave
- Electromagnetic Waves
- Mechanical waves
- Matter Waves
- Electromagnetic Waves
- Properties of Waves
The major properties of waves are:
Amplitude – A wave is an energy propagation phenomenon where the height of the wave is called amplitude, which is usually measured in metres.
Wavelength – In the adjacent cycles of wave crests, the distance between identical points is called a wavelength. It is also measured in metres.
Period – The time required by a particle on a medium to complete one vibrational cycle is known as the period of a wave. The period is measured in time units, such as seconds or minutes.
Frequency – The number of waves passing a point in a specific time is known as the frequency of a wave. The unit of frequency is hertz (Hz) which is equivalent to one wave per second.
The reciprocal of the frequency and vice versa is the period of a wave.
Period=1/Frequency
OR
Frequency=1/Period
Speed – The distance travelled by a given point on the wave (crest) in a given interval of time is the speed of a wave. That is Speed = Distance/Time.
Important Questions on Waves
1) Which of the following waves can be transmitted through the media of solids, liquids and gases?
a) Electromagnetic waves
b) Transverse waves
c) Longitudinal waves
d) Mechanical waves
Correct Option: (c)
Explanation: The changes in the volume and density of the medium are involved in longitudinal waves. Longitudinal waves can be transmitted through all three types of media, i.e. solids, liquids and gases because all these media can tolerate compressive stress.
2) Name the type of wave in which the medium particles vibrate in a direction perpendicular to the direction of wave motion.
a) Longitudinal waves
b) Transverse waves
c) Electromagnetic waves
d) Propagated waves
Correct Option: (b)
Explanation: Particles of the medium in transverse waves vibrate in a direction perpendicular to the wave.
3) A motorboat sailing on water produces what kind of wave?
a) Electromagnetic
b) Mechanical
c) Stationary
d) Longitudinal and transverse
Correct Option: (d)
Explanation: Due to the vibrations of the rudder, longitudinal waves are produced inside water, and transverse waves are generated on the water surface.
4) Identify the property of a wave propagating in a medium independent of the others.
a) Wavelengths
b) Velocity
c) Frequency
d) All of these
Correct Option: (c)
Explanation: Since wave velocity = frequency × wavelength; therefore, the frequency remains unaffected while velocity and wavelength and co-dependent.
5) A boat at anchor is rocked by waves whose velocity is 20m/s and crests are 200m apart. The boat bounces up once in every_____.
a) 500s
b) 20s
c) 10s
d) 0.25s
Correct Option: (c)
Explanation: ÊŽ=200m, v=20m/s
T=ÊŽ/v=200/20 = 10s.
6) Why can lights travel in a vacuum but not sound?
a) Light waves are dual in nature
b) Due to the electromagnetic nature of light waves.
c) Due to the electromagnetic nature of sound waves.
d) Speed of sound is very slow than light
Correct Option: (b)
Explanation: Light waves are electromagnetic; that is why they can travel in a vacuum.
7) In air, the velocity of sound is ________.
a) Slower in dry air than in moist air
b) Directly proportional to the pressure
c) Directly proportional to temperature
d) None of these
Correct Option: (c)
Explanation: The velocity of sound is independent of pressure, but it is proportional to temperature, and hence it increases with humidity.
8) Which parameter does not change when sound travels from air to water?
a) Temperature
b) Velocity
c) Frequency
d) Wavelength
Correct Option: (c)
Explanation: When sound travels from air to water, the frequency remains unchanged.
9) In Doppler’s effect, the apparent frequency does not depend upon _____.
a) Speed of the source
b) Distance between the source and observer
c) Speed of the observer
d) Frequency of the source
Correct Option: (b)
Explanation: Apparent frequency in Doppler’s effect does not depend on the distance between observer and source. But it depends on the frequency of the source, direction and velocity of the source and observer.
10) Calculate the frequency of a sinusoidal wave if the time required for a particular point is 0.107 sec. to move from maximum displacement to zero displacements.
a) 0.72Hz
b) 0.28Hz
c) 2.47Hz
d) 1.47Hz
Correct Option: (d)
Explanation: From maximum displacement to zero displacement, the time required will be:
T/4=0.170s or T=0.68s
Frequency,
v=1/T=1/0.67=1.47Hz.
Practice Questions
1) Define longitudinal waves.
2) Define transverse waves.
3) What are mechanical waves?
4) Give some examples of transverse and longitudinal waves.
5) What are electromagnetic waves?
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