Answer:
Time will be 19 ms so option (a) is correct option
Explanation:
We have given that mass of wire m = 50 gram = 0.5 kg
Frequency f = 810 Hz
Wavelength = 0.4 m
Velocity is given by

Amplitude is given as d = 6 m
So time 
So option (a) is correct option
according to the question are microwaves and X-rays
8.6 cm
Explanation:
Step 1:
In this we have to find the focal length of converging lens.
To find focal length we have,

where u = Object distance
v= Image distance
f = Focal length
Step 2:

(1/f) = 0.116
f = 1/0.116
f = 8.6 cm