Answer:
a) 
b) 
Explanation:
Given:
String vibrates transversely fourth dynamic, thus n = 4
mass of the string, m = 13.7 g = 13.7 × 10⁻¹³ kg
Tension in the string, T = 8.39 N
Length of the string, L = 1.87 m
a) we know

where,
= wavelength
on substituting the values, we get

or

b) Speed of the wave (v) in the string is given as:

also,

equating both the formula for 'v' we get,

on substituting the values, we get

or

or

Explanation:
my guess is A
emission spectrum of a chemical element or chemical compound is the spectrum of frequencies of electromagnetic radiation emitted due to an atom or molecule making a transition from a high energy state to a lower energy state.
15 number of division on Vernier scale and 12 cm on the main scale means 13.2 cm of the object thickness.
<h3>What is value of 15 division of Vernier scale generally?</h3>
A Vernier scale has 10 divisions and the total length of these 10 divisions is equal to the length of 9 divisions of the main scale that equals to 9 mm so in this way 15 number of division on Vernier scale means 14 divisions on the main scale which is equals to 14 mm and we know that there is 12 cm on the main scale so by adding 12 cm and 14 mm we get the 13.2 cm reading of the object thickness. Vernier caliper is a measuring device that comprise of a main scale and a sliding jaw with an attached Vernier.
So we can conclude that 15 number of division on Vernier scale and 12 cm on the main scale means 13.2 cm of the object thickness.
Learn more about Vernier here: brainly.com/question/24694454
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