Progressive and Stationary Waves
A student investigates stationary waves using microwaves.
1.
Figure 1 shows a metre ruler fixed to a bench. The student places a microwave transmitter T at
one end of the ruler and a vertical metal reflector R at the other end. R is at a right angle to the
ruler.
Figure 1
The student places a microwave detector D approximately one-third of the distance from T to R.
When T is switched off, the microammeter connected to D reads zero.
When T is switched on, stationary waves are produced between T and R, and the microammeter
registers a current. When the student moves D along the ruler, the size of the current changes
between maximum and minimum values.
The student measures the current at different positions of D along the ruler to identify a position
P of the minimum current.
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,Progressive and Stationary Waves
Figure 2 is a plot of the measurements taken near P.
Figure 2
(a) Draw a line of best fit for these data.
(2)
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,Progressive and Stationary Waves
(b) State a value for the position of P.
position of P = _______________ cm
(1)
The student moves D along the metre ruler towards R and observes a series of maximum and
minimum readings on the microammeter. He identifies Q as the position of the 8th minimum
current from P. He measures the distance PQ to be 50.9 cm, as shown in Figure 3.
Figure 3
(c) The absolute uncertainty in identifying any minimum current is ± 0.2 cm.
Determine the percentage uncertainty in the distance PQ.
percentage uncertainty in PQ = _______________ %
(2)
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, Progressive and Stationary Waves
(d) Deduce the frequency of the microwaves produced by T.
frequency = _______________ Hz
(3)
(e) Figure 4 shows D placed at a position where the current is a maximum.
Figure 4
The student rotates D by 90°, without changing its distance from T, to the position shown in
Figure 5. The current is now zero.
Page 4 of 50
A student investigates stationary waves using microwaves.
1.
Figure 1 shows a metre ruler fixed to a bench. The student places a microwave transmitter T at
one end of the ruler and a vertical metal reflector R at the other end. R is at a right angle to the
ruler.
Figure 1
The student places a microwave detector D approximately one-third of the distance from T to R.
When T is switched off, the microammeter connected to D reads zero.
When T is switched on, stationary waves are produced between T and R, and the microammeter
registers a current. When the student moves D along the ruler, the size of the current changes
between maximum and minimum values.
The student measures the current at different positions of D along the ruler to identify a position
P of the minimum current.
Page 1 of 50
,Progressive and Stationary Waves
Figure 2 is a plot of the measurements taken near P.
Figure 2
(a) Draw a line of best fit for these data.
(2)
Page 2 of 50
,Progressive and Stationary Waves
(b) State a value for the position of P.
position of P = _______________ cm
(1)
The student moves D along the metre ruler towards R and observes a series of maximum and
minimum readings on the microammeter. He identifies Q as the position of the 8th minimum
current from P. He measures the distance PQ to be 50.9 cm, as shown in Figure 3.
Figure 3
(c) The absolute uncertainty in identifying any minimum current is ± 0.2 cm.
Determine the percentage uncertainty in the distance PQ.
percentage uncertainty in PQ = _______________ %
(2)
Page 3 of 50
, Progressive and Stationary Waves
(d) Deduce the frequency of the microwaves produced by T.
frequency = _______________ Hz
(3)
(e) Figure 4 shows D placed at a position where the current is a maximum.
Figure 4
The student rotates D by 90°, without changing its distance from T, to the position shown in
Figure 5. The current is now zero.
Page 4 of 50
