4.3 Wave Characteristics

Superposition occurs when two or more waves interfere with each other.

   (ii)      Sketch a diagram to support your answer to part (i).

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Superposition is often demonstrated using water waves which are transverse and clearly show increases and decreases in amplitude.

Two microwave transmitters are placed 15 cm apart and connected to the same source. A receiver is placed 70 cm away and moved along a line parallel to the transmitters. The receiver detects and alternating pattern of maxima and minima.

One transmitter is removed and a metal grille is placed between the transmitter and the receiver. The grille is rotated through 180^o and back round again. The signal at the receiver is heard to rise and fall as the grill rotates.

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         (ii)         Sketch a graph to show the pattern of rising and falling signal.

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The analyser is used to investigate polarised light. Light with intensity 11.94 W m⁻² is incident on a polarising filter. The transmission axis of the analyser is fixed at an angle of 35º to the electric field of the polarised light.

(c)     

(i)        Write down the intensity of the light transmitted by the polarising filte

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    (ii)        Calculate the intensity of the light transmitted by the analyser

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The analyser is rotated through 180^o.

Sketch a graph to show the variation of intensity I₂ with angle θ of the light leaving the analyser.

A microwave transmitter is set up 75 cm away from a receiver which is connected to an oscilloscope so that the intensity of the wave incident on the receiver can be determined.

Initially the intensity is found to be 32 mW m⁻². The receiver is moved to a new position 125 cm from the transmitter. The new intensity is found to be 11.6 mW m⁻². 

The transmitter remains at 125 cm and the energy of the signal is increased. The new intensity is found to be 46.4 mW m⁻².

Radio waves are emitted from a straight conducting rod antenna such that the plane of polarisation of the waves is parallel to the rod. An identical metal conducting rod, known as an aerial, is used for reception.

The receiving aerial is moved so that it leans 22^o from its original position. The power of the received signal in the new position is 15 μW.     

A group of hikers are exactly equidistant between two radio transmitters, X and Y. The transmitters are set to an operating wavelength of 200 m and have the same power outputs.

Once at Q they turn and walk towards Y, continuing until they receive a signal with amplitude double that emitted from either transmitter.

(i)         Explain why there is no increase in amplitude detected on the walk from P to Q

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(ii)        Calculate the distance they walked along the line from Q to Y

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The hikers continue moving from Q towards the transmitter at Y where the distance QY is 20 km. The signal continues to rise and fall as they walk.

The hikers are wearing polarising glasses to protect their eyes from glare.

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