Electrostatic Potential and Capacitance — Physics STD 12 Science — Question

Two resistors R and 2R are connected in series in an electric circuit. The thermal energy developed in R and 2R are in the ratio:

1. 1 : 2.
2. 2 : 1.
3. 1 : 4.
4. 4 : 1.

Assertion  :  Microwave communication is preferred over optical communication.

Reason      : Microwaves provide large number of channels and band width compared to optical signals.

(a) If both assertion and reason are true and the reason is the correct explanation of the assertion.

(b) If both assertion and reason are true but reason is not the correct explanation of the assertion.

(c) If assertion is true but reason is false.

(d) If the assertion and reason both are false.

The work done in carrying a charge of 5μC  from a point A to a point B in an electric field is 10mJ.  The potential difference (  is then

(a) + 2kV

(b) – 2 kV

(c) + 200 V

(d) – 200 V

The de-Broglie wavelength of an electron having 80eV of energy is nearly  (1eV = 1.6 × 10^–19 J,  Mass of electron = 9 × 10^–31kg  Plank’s constant = 6.6 × 10^–34 J-sec)

(a) 140 Å

(b) 0.14 Å

(c) 14 Å

(d) 1.4 Å

If the wavelength of light in an experiment on photoelectric effect is doubled:

1. Photoelectric emission will not take place.
2. Photoelectric emission may or may not take place.
3. The stopping potential will increase.
4. The stopping potential will decrease.

The photoelectric threshold wavelength for potassium (work function being 2eV ) is

(a) 310 nm

(b) 620 nm

(c) 1200 nm

(d) 2100 nm

When the wave of hydrogen atom comes from infinity into the first orbit then the value of wave number is

(a) 109700 cm–1

(b) 1097cm–1

(c) 109 cm–1

(d) None of these

On heating a liquid, the refractive index generally

(a) Decreases

(b) Increases or decreases depending on the rate of heating

(c) Does not change

(d) Increases

The light source will be coherent if :