Physics

Which ONE of the following is the correct definition of the principle of superposition?

Which ONE of the following is the correct definition of destructive interference?

Which ONE of the following is the correct definition of frequency?

Which ONE of the following is the correct definition of a transverse wave?

Which ONE of the following is the correct definition of wave speed?

The rest position of a rope lies along the x-axis of a displacement–position graph. Successive crests of the wave are at x = 0,15 m and x = 0,75 m, with a trough at x = 0,45 m. What is the wavelength of the wave?

A displacement–time graph for one particle of a skipping rope shows troughs at t = 0,12 s and t = 0,52 s. What is the period of the wave?

A displacement–position graph of a wave on a washing line shows two successive troughs at x = 20 cm and x = 140 cm. What is the wavelength in metres?

A displacement–position graph of a wave on a slinky shows a crest at x = 0,10 m and the very next trough at x = 0,55 m. What is the wavelength?

On a displacement–time graph for a particle on a spring, the particle is at its highest point at t = 0,05 s and next at its lowest point at t = 0,17 s. What is the period of the wave?

A transverse wave on a rope has a wavelength of 1,2 m. Four points lie on the rope at A: x = 0,2 m; B: x = 0,8 m; C: x = 1,4 m; D: x = 1,7 m. Which two points are in phase with each other?

A wave on a rope has a wavelength of 0,80 m and a crest at x = 0,20 m. At which position is there also a point in phase with this crest?

Two points P and Q on a rope wave of wavelength 0,60 m both have zero displacement at this moment. P is at x = 0,10 m and moving upward. Q is at x = 0,40 m and moving downward. Which statement is correct?

Points A, B, C, D and E lie in order along a rope wave. A, C and E are crests; B and D are troughs. Which TWO points are in phase with A?

A wave on a rope has a wavelength of 0,50 m. Which pair of points on the rope are in phase with each other?

On a long spring, pulse P (amplitude 5 cm, upward) meets pulse Q. At complete overlap the spring is displaced 8 cm upward. What are the amplitude and direction of pulse Q?

On a rope, an upward pulse P of amplitude 6 cm meets pulse Q. At complete overlap the rope is displaced 2 cm upward. What are the amplitude and direction of pulse Q?

A pulse P of amplitude 3,5 cm (upward) meets a pulse Q on a stretched spring. At complete overlap the spring is displaced 1,5 cm downward. What are the amplitude and direction of pulse Q?

A pulse P of amplitude 4 cm is inverted (downward). It meets a pulse Q, and at complete overlap the rope is displaced 7 cm downward. What are the amplitude and direction of pulse Q?

On a washing line, an upward pulse P of amplitude 2,5 cm meets pulse Q. At complete overlap the line is momentarily flat. What are the amplitude and direction of pulse Q?

A vibrating blade is clamped to one end of a long string. It completes one vibration in 20 ms and the waves it sends along the string are 30 cm long. At what speed, in m·s⁻¹, do the waves travel along the string?

A learner shakes a long spring at 8,0 Hz and the waves travel at 360 cm·s⁻¹. What is the wavelength of the waves, in metres?

A pulse takes 0,40 s to travel 3,6 m along a rope. The rope is then shaken at 6,0 Hz. What is the wavelength of the waves?

The distance from the first crest to the fourth crest of a wave on a spring is 1,8 m. The source vibrates 5,0 times every second. What is the speed of the wave?

Waves on a rope travel at 1,5 m·s⁻¹. A learner wants waves with a wavelength of 25 cm. At what frequency must she shake the rope?

A wave on a rope has a frequency of 2,0 Hz and a wavelength of 0,80 m. The learner now shakes the same rope at 5,0 Hz. Which row gives the new wave speed and wavelength?

A wave on a long spring has a frequency of 6,0 Hz and a wavelength of 0,25 m. The learner halves the frequency and keeps the same spring. Which row gives the new wave speed and wavelength?

Waves of frequency 4,0 Hz travel along a rope at 3,0 m·s⁻¹. The learner wants waves with a wavelength twice as long on the same rope. What frequency should she use?

A pulse of waves needs 4,0 s to travel the whole 12 m of a rope while the learner shakes it at 3,0 Hz. She now shakes it at 6,0 Hz. Which row gives the time to travel the rope and the new wavelength?

A rope wave has a period of 0,50 s and a wavelength of 0,90 m. The learner shakes the same rope so that the period becomes 0,30 s. Which row gives the new wave speed and wavelength?

A learner flicks one end of a long, stretched spring once, so that a single transverse pulse travels along it. A second pulse is then sent from the other end. Both pulses are upward, each with an amplitude of 3 cm, and they overlap exactly. (a) Define the term pulse. (2) (b) Define the term amplitude. (2) (c) Name the type of interference that occurs and determine the amplitude of the resultant pulse at complete overlap. (2)

1. Content: a pulse is a single disturbance'Single' is the word that separates a pulse from a wave. 'A wave' or 'a movement' alone does not earn it.
2. Content: ... in a mediumThe second half of the 2-mark definition: a disturbance needs a medium (the spring) to travel in.
3. Content: amplitude is the maximum displacement'Maximum' is the key word. 'Height of the wave' or 'size of the pulse' is a description, not the definition.
4. Content: ... of a particle from its rest (equilibrium) positionThe reference point matters. Displacement is measured from the rest line, not from the trough to the crest.
5. Content: constructive interference (crest meets crest)Two upward pulses are crest on crest, so the name is constructive. Destructive here shows the two cases were swapped.
6. Accuracy: resultant amplitude = 3 + 3 = 6 cmThe disturbances add: (+3) + (+3) = +6 cm. The answer mark needs the 6 cm; the 1,5 cm average is a common wrong value.

(a) A pulse is a single disturbance in a medium. (b) Amplitude is the maximum displacement of a particle of the medium from its rest (equilibrium) position. (c) The crest of one pulse overlaps with the crest of the other, so this is constructive interference. The disturbances add, so the resultant amplitude is 3 + 3 = 6 cm, upward, and then both pulses carry on unchanged.

Two graphs describe the same transverse wave on a rope. Displacement–position graph: the rest position is at 0 cm, crests of displacement 4 cm are at x = 15 cm and x = 105 cm, and a trough of displacement −4 cm is at x = 60 cm. Displacement–time graph for one particle of the rope: crests at t = 0,05 s and t = 0,45 s. (a) Write down the amplitude of the wave. (1) (b) Determine the wavelength of the wave, in metres. (2) (c) Determine the period of the wave. (1) (d) Calculate the speed of the wave. (3)

1. Accuracy: amplitude = 4 cmWrite down: one reading with its unit. The amplitude is measured from the rest line, so 4 cm. The peak-to-peak 8 cm is the trap.
2. Method: wavelength = distance between successive crests = 105 − 15Determine shows the working. Two successive crests are one wavelength apart; the crest-to-trough 45 cm is only half.
3. Accuracy: λ = 90 cm = 0,90 mThe question asks for metres, so the centimetres must be converted. 90 on its own, or 90 m, loses the mark.
4. Accuracy: period T = 0,45 − 0,05 = 0,40 sSuccessive crests on a displacement-time graph are one period apart. The unit is part of the mark.
5. Method: f = 1/T = 1/0,40 = 2,5 HzThe speed equation needs a frequency, and the graph gave a period. Skipping this step is the commonest way to lose the calculation.
6. Method: v = fλ = (2,5)(0,90)Formula and substitution with SI values. A wrong f or λ carried over from earlier, used correctly here, still earns this mark (consistent accuracy).
7. Consistent accuracy: v = 2,25 m·s⁻¹ with the unitThe value and the unit together. 2,25 on its own, or 225 left in cm·s⁻¹, loses the mark.

(a) Amplitude = 4 cm, measured from the rest line to a crest. (b) The wavelength is the distance between successive crests: λ = 105 − 15 = 90 cm = 0,90 m. (c) Successive crests are one period apart: T = 0,45 − 0,05 = 0,40 s. (d) f = 1/T = 1/0,40 = 2,5 Hz. v = fλ = (2,5)(0,90) = 2,25 m·s⁻¹.

Waves on a stretched rope have a period of 80 ms and a wavelength of 24 cm. (a) Calculate the frequency of the waves. (2) (b) Calculate the speed of the waves in m·s⁻¹. (2) (c) The learner now shakes the same rope at 25 Hz. State the new wave speed, with a reason, and calculate the new wavelength. (3)

1. Method: convert T = 80 ms = 0,080 s, then f = 1/T = 1/0,080The conversion and the reciprocal are the method. Using 80 instead of 0,080 gives 0,0125 Hz.
2. Accuracy: f = 12,5 HzValue and unit together. 12,5 without Hz does not earn the mark.
3. Method: v = fλ = (12,5)(0,24), with 24 cm converted to metresThe wavelength must be in metres before the substitution. (12,5)(24) = 300 is in the wrong unit and loses the answer mark too.
4. Accuracy: v = 3,0 m·s⁻¹12,5 × 0,24 = 3,0 exactly. The unit m·s⁻¹ is part of the mark.
5. Content: the speed is unchanged (3,0 m·s⁻¹) because the medium (the same rope) sets the speedThis is the idea the whole topic turns on: shaking faster does not make the wave faster. The reason, the same rope, is the mark.
6. Method: λ = v/f = 3,0 ÷ 25Rearranging v = fλ with the unchanged speed. If you carried a wrong speed from (b), this mark is still yours (consistent accuracy).
7. Consistent accuracy: λ = 0,12 mFrequency doubled, wavelength halved: 0,24 m becomes 0,12 m. The unit is part of the mark.

(a) T = 80 ms = 0,080 s, so f = 1/T = 1/0,080 = 12,5 Hz. (b) v = fλ = (12,5)(0,24), with 24 cm = 0,24 m = 3,0 m·s⁻¹. (c) The speed is unchanged, still 3,0 m·s⁻¹, because it is the same rope and the medium sets the wave speed. λ = v/f = 3,0 ÷ 25 = 0,12 m, half the earlier wavelength because the frequency has doubled.

Explain to a Grade 8 learner what the amplitude and the wavelength of a wave mean on a drawing of the wave, and how you can tell which two points on the drawing are in phase.

Explain to a Grade 8 learner why a measurement such as '24 cm' and '80 ms' must be changed before you can work out how fast a wave is travelling, and show the steps.

Explain to a Grade 8 learner why a big flick and a small flick of the same rope make pulses that reach the other end at the same time, and what is different about them.