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CIE AS/A Level Physics 7.1 Progressive waves Study Notes

CIE AS/A Level Physics 7.1 Progressive waves Study Notes- 2025-2027 Syllabus

CIE AS/A Level Physics 7.1 Progressive waves Study Notes – New Syllabus

CIE AS/A Level Physics 7.1 Progressive waves Study Notes at  IITian Academy  focus on  specific topic and type of questions asked in actual exam. Study Notes focus on AS/A Level Physics latest syllabus with Candidates should be able to:

  1. describe what is meant by wave motion as illustrated by vibration in ropes, springs and ripple tanks
  2. understand and use the terms displacement, amplitude, phase difference, period, frequency, wavelength and speed
  3. understand the use of the time-base and y-gain of a cathode-ray oscilloscope (CRO) to determine frequency and amplitude
  4. derive, using the definitions of speed, frequency and wavelength, the wave equation v = f λ
  5. recall and use v = f λ
  6. understand that energy is transferred by a progressive wave
  7. recall and use intensity = power/area and intensity ∝ (amplitude)2 for a progressive wave

AS/A Level Physics Study Notes- All Topics

Exam Style QuestionsNew

7.1.1 describe what is meant by wave motion as illustrated by vibration in ropes, springs and ripple tanks

  • Wave is a method of propagation of energy.
  • It represents a disturbance in a medium that carries energy without actual motion of particles. 
  • For example, when we drop a pebble into a pond of still water, a few circular ripples move outwards, on the surface of the water. As these circular ripples spread out, energy is being carried with them.                                                                                 
  •                                                      
  • Slink waves can be made by vibrating the spring back and forth in either a horizontal or a vertical direction. 
  • Similar waves are produced by the movement of rope.

                                                                                 

7.1.2 understand and use the terms displacement, amplitude, phase difference, period, frequency, wavelength and speed

  •                
  • Amplitude is the value of the maximum displacement from the rest of central position in either direction.
  • Frequency (f) refers to the number of complete waves produced per second. The SI unit of frequency is Hertz.
  • Period is the time taken to complete one wave cycle. (T = 1/f)
  • Wavelength (λ) is the shortest distance between any two points on the wave that are in phase. In simple terms, it is the distance between two consecutive crests or troughs.
  • Speed is the distance travelled by the wave per second.
  •                                                       
  • Phase : Two points are said to be in phase if they are moving in the same direction with the same speed and having same displacements from the rest position. Any two crests and troughs are said to be in phase.
  • Phase difference :  It is the difference between the initial angles of two waves.
  • When the crests and troughs of two waves are aligned with each other, they are said to be in phase.
  • The difference is the alignment leads to out of phase nature of waves and is determined using the difference in the initial angle, aka phase difference.

7.1.3 understand the use of the time-base and y-gain of a cathode-ray oscilloscope (CRO) to determine frequency and amplitude

                                               
  • A calibrated cathode ray oscilloscope (CRO) implies that the time base is set such that the period, T, of the oscillations of the air layers detected by the microphone may be read.
  •  The y-axis gives the amplitude of the wave and x-axis give the time period.
  • Frequency can be determined using the relation, f = \(\frac{1}{T}\).
  •                 Given time base is 2 ms cm-1        
  • In this case,  time base is 2 ms cm-1.
  • Now, T = (2 ms cm-1 × 4  cm) = 8.0 ms
  • Frequency f = 1/(8 × 10-3 ) = 125 Hz. 
 

7.1.4 derive, using the definitions of speed, frequency and wavelength, the wave equation v = f λ

  • Wavelength is the distance moved by the wave in one cycle, i.e., distance.
  • Time = 1/Frequency.
  • Speed = \(\frac{Distance}{time}\)
  • Thus, v = \(\frac{λ}{1/f}\) = λf.

7.1.5 recall and use v = f λ

Question

Visible light has wavelengths between 400 nm and 700 nm, its speed in vacuum is 3 × 108 m/s. What is the maximum frequency of visible light?

Answer/Explanation

v = λf.

For maximum frequency, wavelength should be minimum.

Therefore, fmax = v/λmin.

= (3 × 108)/(400× 10-9 )= 7.5 × 108 Hz.

 

7.1.6 understand that energy is transferred by a progressive wave

                                             
  • A wave in which energy is transferred from one place to another as a result of its motion is called a progressive wave.
  • For example : An ultraviolet light wave, which transfers energy from the sun to the skin of people lying on the beach, for instance, is a progressive wave. In general, waves that move from one point to another transfer some kind of energy.
  • In a progressive wave, the shape of the wave itself, is what is transferred, not the actual components of the medium.
  • Sound waves: When a sound wave is propagated from a tuning fork to an ear of a person some distance away, he vibrations of the fork sets the air layer next to the fork into vibrations.
  • The second layers is set into vibration due to the transfer of energy from the first layer. This process continues to the subsequent layers ultimately setting the ear drum to vibrations enabling the person to hear the sound of the fork via energy transfer.

7.1.7 recall and use intensity = power/area and intensity ∝ (amplitude)2 for a progressive wave

  • Intensity refers to the rate of incidence of energy per unit area normal to the direction of incidence.
  • The rate of incidence of energy is referred  as the power.
  • Thus, I = \(\frac{P}{A}\) with SI unit W\(m^{-2}\).
  • Intensity ∝ (Power) implying intensity ∝ (Amplitude)2.

Introducing Waves

  •  Waves carry energy.
    • For Example, during an earthquake, the seismic waves produced can cause great damage to buildings and the surroundings.
  • What is a wave?
    •  Wave is a method of propagation of energy.
      For example, when we drop a pebble into a pond of still water, a few circular ripples move outwards, on the surface of the water. As these circular ripples spread out, energy is being carried with them.

Sources of Waves

  •  The source of any wave is a vibration or oscillation.
  •  For example, the forming of the slinky waves as shown.
    • Wave motion provides a mechanism for the transfer of energy from one point to another without the physical transfer of the medium between the two points.

                                                                                                                        

Slink waves can be made by vibrating the firt coil back and forth in either a horizontal or a vertical direction.

Two Types of Waves

• Transverse Wave Rope waves, Water waves, Light waves, Radio waves, Electromagnetic waves.
• Longitudinal Wave Sound waves and waves produced in a vertical oscillating spring under tension.

                                             

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