Download App

Electric Charges and Fields — Physics STD 12 Science — Question

Bihar BoardEnglish MediumSTD 12 SciencePhysicsElectric Charges and Fields3 Marks
Question
Suppose an attractive nuclear force acts between two protons which may be written as $\text{F}=\text{Ce}^{-\text{kr}}/\text{r}^2.$
  1. Write down the dimensional formulae and appropriate SI units of C and k.
  2. Suppose that k = 1 fermi-1 and that the repulsive electric force between the protons is just balanced by the attractive nuclear force when the separation is 5 fermi. Find the value of C.
✓

Answer

Expression of electrical force $\text{F}=\text{C}\times\text{e}^{\frac{-\text{kr}}{\text{r}^2}}$

Since e-kr is a pure number. So, dimensional formulae of $\text{F}=\frac{\text{dimensional formulae of C}}{\text{dimensional formulae of r}^2}$

Or, $\big[\text{MLT}^{-2}\big]\big[\text{L}^2\big]=$ dimensional formulae of $\text{C}=\big[\text{ML}^3\text{T}^{-2}\big]$

Unit of C = unit of force × unit of r2 = Newton × m2 = Newton-m2

Since -kr is a number hence dimensional formulae of

$\text{k}=\frac{1}{\text{dim entional formulae of r}}=\big[\text{L}^{-1}\big]$ Unit of k = m-1

Need a full question paper?

Generate a complete, print-ready paper with questions like this in minutes — across 16+ boards, with answer keys.

Start Generating Free

Explore more

More "3 Marks Question" from Electric Charges and Fields→Electric Charges and Fields — all question types→Physics STD 12 Science question papers→Bihar Board STD 12 Science question papers→Bihar Board question paper generator→

Similar questions

Draw the intensity distributions for (i) the fringes produced in interference, and (ii) the diffraction bands produced due to single slit. Write two points of difference between the phenomena of interference and diffraction.
→
Explain the de-Broglie wavelength by explaining the waveform of matter.
→
A square plate of mass 120g and edge 5.0cm rotates about one of the edges. If it has a uniform angular acceleration of 0.2rad/s2, what torque acts on the plate?
→
A traffic policeman sounds a whistle to stop a car-driver approaching towards him. The car-driver does not stop and takes the plea in court that because of the Doppler shift, the frequency of the whistle reaching him might have gone beyond the audible limit of 20kHz and he did not hear it. Experiments showed that the whistle emits a sound with frequency close to 16kHz. Assuming that the claim of the driver is true, how fast was he driving the car? Take the speed of sound in air to be 330m/s. Is this speed practical with today's technology?
→
A laser beam has intensity 2.5 × 1014Wm-2. Find amplitudes of electric and magnetic fields in the beam.
→
a. Using the Bohr's model, calculate the speed of the electron in a hydrogen atom in the n = 1, 2 and 3 levels.
b. Calculate the orbital period in each of these levels.
→
If this telescope is used to view a 100 m tall tower 3 km away, what is the height of the image of the tower formed by the objective lens?
→
  1. How does one explain the emission of electrons from a photosensitive surface with the help of Einstein's photoelectric equation?
  2. The work function of the following metals is given: Na 2.75 ev, K = 2.3 eV, Mo = 4.17 eV and Ni = 5.15 eV. Which of these metals will not cause photoelectric emission for radiation of wavelength 3300 Å from a laser source placed 1 m away from these metals? What happens if the laser source is brought nearer and placed 50 cm away?
→
  1. The refractive index of glass is 1.5. What is the speed of light in glass? (Speed of light in vacuum is 3.0 × 108 ms–1).
  2. Is the speed of light in glass independent of the colour of light? If not, which of the two colours red and violet travels slower in a glass prism?
→
A semiconductor has equal electron and hole concentration of 2 × 108/m3. On doping with a certain impurity, the hole concentration increases to 4 × 1010/m3.
  1. What type of semiconductor is obtained on doping?
  2. Calculate the new electron and hole concentration of the semiconductor.
  3. How does the energy gap vary with doping?
→