Answer:
option D
Explanation:
given,
Intensity of sound = 20 dB
distance = 15 m
intensity of sound is increased to = 50 dB
distance between the sound level = ?
Using relation
L₁ = 20 dB L₂ = 50 dB r₁ = 15 m r₂ = ?
r₂ = 0.47 m
r₂ = 47 cm
hence, the correct answer is option D
1)
The electrostatic force between two charges is given by
(1)
where
k is the Coulomb's constant
q1, q2 are the two charges
r is the separation between the charges
When the two spheres are brought in contact with each other, the charge equally redistribute among the two spheres, such that each sphere will have a charge of
where Q is the total charge between the two spheres.
So we can actually rewrite the force as
And since we know that
r = 1.41 m (distance between the spheres)
(the sign is positive since the charges repel each other)
We can solve the equation for Q:
So, the final charge on the sphere on the right is
2)
Now we know the total charge initially on the two spheres. Moreover, at the beginning we know that
(we put a negative sign since the force is attractive, which means that the charges have opposite signs)
r = 1.41 m is the separation between the charges
And also,
So we can rewrite eq.(1) as
Solving for q1,
Since , we can substituting all numbers into the equation:
which gives two solutions:
Which correspond to the values of the two charges. Therefore, the initial charge q1 on the first sphere is