Question

The distance between $1^{st}$ crest and $7^{th}$ through of a transverse wave of wavelength 20 cm is ____________.

• A. 100 cm
• B. 110 cm
• C. 120 cm
• D. 130 cm

Answer 1

The correct option is D 130 cm

Distance between $1^{st}$ crest and $7^{th}$ crest $=6\lambda$
Distance between $7^{th}$ crest and $7^{th}$ through $=\frac{\lambda }{2}$
$\therefore$ Distance between $1^{st}$ crest and $7^{th}$ through
$=6\lambda +\frac{\lambda }{2}$
$=\frac{13\lambda }{2}=\frac{13\times 20}{2}=130cm$