Exam Style Answers 14 Asal Physics CB

 

 

CAMBRIDGE INTERNATIONAL AS & A LEVEL PHYSICS: COURSEBOOK 

Exam-style questions and sample answers have been written by the authors. In examinations, the way marks are awarded may be different.

 Coursebook answers Chapter 14 b

Exam-style questions 1

A 

 

Longitudinal waves, e.g. sound, can also produce stationary waves. So, this statement is incorrect. All the other statements are correct about stationary waves.

  2

[1]

C 

a b

=

×

 ii ii

[1]

 

[1]

 

 λ

A

c 4

a

N

A

c

 

A

There would be double the number of loops (6).  [1] Resonance is when the frequency of one source of vibration coincides with the natural frequency of vibration of a body, causing the body to vibrate with a large amplitude.   [1]

N

A

A

pulley

N A

N A

A

slotted masses

=

Node and antinode marked  Wavelength marked 

N

A

cm; v   f   f  λ   120  0.390  46.8 m s −1 =

 

75 cm N

[1]

 λ    = 39.0

3

i vibrator

6

a

=

×

=

=

=

−

Speed of the waves down the string changes (with tension)  so wa wavelength velength changes  Vibrating   i    ii ii

b

Any one node and any one antinode shown.  [2] 75 wavelength    cm  [1] 3  λ    120 0.7 c   f   f  [1] 755   3 c   30 m s 1  [1]

  5

a

       

 

1

λ  =

[1] 4    0.312 m   λ = 256 × 4 × 0.312 = 319 ≈ 320 m s 1  [1] v = f   f 

7

a

−

Similarities: Points in the waves vibrate   [1]  λ  The wave speed  f   f  [1] Differences: A progressive wave transf transfers ers energy; a standing waves does not transfer energy.  [1] Points in a progressive wave have different amplitudes of vibration with respect to time; points of a standing wave have have the same amplitude with respect to time.  [1]

3 4  λ = 63.8

[1]

cm 

[1]

 v = f   f  λ = 400 ×  43  × 0.638 

[1]

 sspeed peed of sound  340 m s−1  The waves have a constant phase i difference 

[1]

 

[1]

 ii ii

=

  b

[1]

back and forth parallel to the tube  [1] Stationary  [1]

=

b

[1]

i

 

over a period of time.  The amount by which one wave leads or lags another  expressed using phase angle. 

[1]

[1] [1]

Maxima occur when the reflected waves wa ves are exactly in phase with the incident wave.  [1] Minima occur when the reflected waves are 180° out of phase with the incident wave.  [1]

Cambridge International AS & A Level Physics – Sang, Jones, Chadha & Woodside © Cambridge University Press 2020

   

CAMBRIDGE INTERNATIONAL AS & A LEVEL PHYSICS: COURSEBOOK 

 ii ii

Each time the wa wave ve amplitude falls to zero, the plate has moved through 12  λ 42.0   2.5  16.8 cm   λ leading to f     c   f   f 

 λ = 

 

   

=

=

3 108 ×

=

×

16.8 10  1.78  10    1.8  109 Hz 

  c

  8

a

 

 

=

×

9

≈

×

−

 

[1]

 f     = 210 ×  1.4 = 248.5 Hz 

[1]

[1]

 aabsolute bsolute uncertainty   1 2    0.08  248.5  9.94 Hz 

[1]

 f  = 250 ± 10 Hz  

[1]

[1]

2

[1] [1]

7  × λ  λ = 90 cm so λ = 51.4 cm  4  f  λ = 512 × 51.4 × 10 2  c = f 

[1]

=

×

×

=

(The value must be given to 2 sig. figs and absolute uncertainty given to 1 sig. fig)

[1]

−

 263 m s   1

−

[1] [1]

  c

Any two correct points 

 

[1]

 f     ∝ v ∝ √T 

Phase shift of 180°  On reflection 

=

v = f   f  λ and λ = 2L =  constant (L = length of wire)  

[1]

Q no movement  [1] P, R, S and T vibrate from side to side parallel to the tube  [1] P and S ha have ve largest amplitude  [1]

b

2

 

9

[1]

Cambridge International AS & A Level Physics – Sang, Jones, Chadha & Woodside © Cambridge University Press 2020