Q. A particle of mass 1 mg has the same wavelength as an electron moving with a velocity of 3 × 10⁶ m s⁻¹. The velocity of the particle is (mass of electron = 9.1 × 10⁻³¹ kg)
A) 2.7 × 10⁻²¹ m s⁻¹
B) 2.7 × 10⁻¹⁸ m s⁻¹
C) 9 × 10⁻² m s⁻¹
D) 3 × 10⁻³¹ m s⁻¹
Explanation
[Solution from source] Equal de Broglie wavelengths (λ = h/mv) mean equal momenta. 1 mg = 10⁻⁶ kg, so v = (9.1 × 10⁻³¹ × 3 × 10⁶)/10⁻⁶ ≈ 2.7 × 10⁻¹⁸ m s⁻¹. Taking 1 mg as 10⁻³ kg gives 2.7 × 10⁻²¹ m s⁻¹. Answer (2).
Reviewed by Dr. Abubacker
Physics Educator & NEET/JEE Specialist
Ph.D. in Physics with 19+ years of teaching experience.