For a perfectly reflecting surface the photon momentum change is twice the incident momentum, so momentum transferred = 2E/c.
1284
A student connects a photocell to supply and finds that when the cell is exposed to monochromatic radiation, a current flows only when the potential difference across the cell is less than 1.6 V. What is the maximum energy of the emitted electrons?
Stopping potential 1.6 V corresponds to maximum electron energy e×1.6 V ≈ 1.6 eV ≈ 2.56×10^-19 J, so option B (≈2.6×10^-19 J) is correct.
1285
In an atomic bomb, a temperature of about 10 million degrees is developed at the moment of explosion. In what region of the spectrum do the wavelengths corresponding to maximum energy density lie if the light source is in the atomic bomb?
Modulation is the process of imposing a low-frequency information signal onto a high-frequency carrier wave.
1289
A gold leaf electroscope is charged and the leaves are observed to diverge by a certain amount. A beam of X-rays is allowed to fall upon the electroscope for a short period. The effect is that
X-rays ionize air, allowing the electroscope to discharge and causing the leaves to collapse (lose divergence).
1290
Light of frequency 4.5 times the threshold frequency is incident on photo-sensitive material. If the frequency is halved and intensity is doubled, then the photocurrent becomes
Halving frequency leaves it above threshold (4.5→2.25 times threshold) so emission continues; doubling intensity doubles photon flux, hence photocurrent doubles.
