Answer:
68.8 Hz
137.6 Hz, 206.4 Hz
Explanation:
L = Length of tube = 2.5 m
v = Velocity of sound in air = 344 m/s
Distance between nodes is given by

Where n = 0, 1, 2, 3, ...
Making n+1 = n

where n = 1, 2, 3 .....
For fundamental frequency n = 1

Frequency is given by

The fundamental frequency is 68.8 Hz
First overtone

Second overtone

The overtones are 137.6 Hz, 206.4 Hz
Answer:
a. 3.039cm
b.magnetic field is 
Explanation:
Direction of the solenoid magnetic field is along the axis of the solenoid. and magnetic field due to the wire perpendicular to that due to the solenoid.. Magnetic field at r is given by:

Angle of net magnetic field from axial direction is given by:
,
Field due to solenoid:

Field due to wire:

Therefore, r:

Hence, the radial distance is 3.039cm
b.The magnetic field strength is given by:

Hence, the magnetic field is 