Question

Suppose that a guitar string has a length 0f 0.64 m, a mass of 4.3 g ( 0.0043 kg ) and a tension of 75.6 N.

a) What is the mass per unit of length of this string? b) What is the speed of a wave on this string?

a)

b)

E 10: [ Page 406, 9th edition ]

Suppose that a photon has a wavelength of 520 nm (green). a) What is the frequency of this photon? b) What is the energy of this photon in joules ( h – 6.626 × 10 – 34 J.s ).

a)

b)

Answer 1

for the first questions

a) let the mass per unit length is u

mass per unit length = mass/length

mass per unit length = 0.0043/0.64

mass per unit length = 6.72 *10^-3 Kg/m

b) speed of wave on the string = sqrt(T/u)

speed of wave on the string = sqrt(75.6/(6.72 *10^-3))

speed of wave on the string = 106.6 m/s

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a) frequency of photon = speed of light/wavelength

frequency of photon = 3 *10^8/(520 *10^-9)

frequency of photon = 5.77 *10¹⁴ Hz

b)

energy of photon = h * f

energy of photon = 6.626 * 10^-34 * 5.77 *10^14

energy of photon = 3.82 *10^-19 J

the energy of photon is 3.82 *10^-19 J