Light with an average flux of 20 W/cm² falls on a non-reflecting surface at normal incidence having surface area 20 cm². The energy received by the surface during time span of 1 minute is :

An electron is accelerated from rest through a potential difference of V volt. If the de-Broglie wavelength of the electron is 1.227 $$ \times $$ 10^-2 nm, the potential difference is :

An electron is accelerated through a potential difference of 10,000 V. Its de Broglie wavelength is (nearly) : (m_e = 9 $$ \times $$ 10^–31 kg)

An electron of mass m with an initial velocity $$\overrightarrow v = {v_0}\widehat i$$ (v₀ > 0) enters an electric field $$\overrightarrow E = - {\overrightarrow E _0}\widehat i$$ (E₀ = constant > 0) at t = 0. If $$\lambda $$₀ is its de-Broglie wavelength initially, then its de- Broglie wavelength at time t is