In normal adjustment of an astronomical telescope (final image at infinity):

• Tube length $L$ is the sum of focal lengths of objective and eyepiece:
  $$f_o = 10\,\text{m} = 1000\,\text{cm}$$
  $$f_e = 10\,\text{cm}$$
  $$L = f_o + f_e = 1000\,\text{cm} + 10\,\text{cm} = 1010\,\text{cm}$$
• The magnifying power (magnification) in normal adjustment is:
  $$m = \frac{f_o}{f_e} = \frac{1000\,\text{cm}}{10\,\text{cm}} = 100$$

In Bohr's model of the hydrogen atom, the orbital quantities depend on principal quantum number $n$ as follows:

• Radius of $n$-th orbit: $r_n = \frac{\varepsilon_0 h^2 n^2}{\pi m e^2} \propto n^2$. Thus, (A) is false and (D) is true.
• Orbital speed of electron: $v_n = \frac{e^2}{2\varepsilon_0 h n} \propto \frac{1}{n}$. Thus, (B) is true.
• Total energy magnitude: $|E_n| = \frac{m e^4}{8\varepsilon_0^2 h^2 n^2} \propto \frac{1}{n^2}$. Thus, (C) is true.

In a full wave rectifier:

• Both the positive and negative half-cycles of the alternating input voltage are rectified into unidirectional pulses flowing through the load in the same direction.
• Therefore, for every single complete cycle of the AC input voltage, the pulsating DC output completes two pulses.
• The fundamental ripple frequency of the output is twice the input frequency:
  $$f_{\text{out}} = 2 \times f_{\text{in}} = 2 \times 50\,\text{Hz} = 100\,\text{Hz}$$
  (In contrast, a half wave rectifier produces $f_{\text{out}} = f_{\text{in}} = 50\,\text{Hz}$).