Physics Test - 35

In Rutherford's model we have a large massive core called the nucleus whereas, in Thomson's model we do not have. Thus the probability of backward scattering by Thomson's model is much less than that predicted by Rutherford model.

In the Geiger-Marsden experiment very small deflection of the beam was expected because positive charge and the negative electrons are distributed through the whole atom reducing electric field inside the atom.

We use the concept of conservation of energy and distance of closest approach in Rutherford's alpha scattering experiment to find the radius of the nucleus is proportional to the Mass Number. The consequence of this is that the density of the nucleus is a constant, independent of mass number for all nuclei.

For A nucleons

R=R_o​A^1/3 [R_o=constant]

So, R∝A^1/3

The ratio of the volume of the atom and the volume of the nucleus is 10¹⁵

The radius of an atomic nucleus is of the order of 10⁻¹³cm or 10⁻¹⁵m or one Fermi unit.

On the other hand, the radius of an atom is of the order of 10⁻⁸cm or 10⁻¹⁰m or one angstrom unit.

Note:

The radius of the nucleus is much smaller than atomic radius.

The ratio of atomic radius to radius of nucleus is 10⁻¹⁰m /10⁻¹⁵m ​=10⁵

Volume is proportional to cube of radius.

The ratio of atomic radius to radius of nucleus is (10⁵)³=10¹⁵

Photoelectrons will come out from the surface of the metal only if it gets enough energy during the irradiation the energy needed depends on the metal and the max energy that can be provided on the light.

Voltage across the electrodes of a cathode ray gun, V=500V

Charge of the electron=1.6x10^-19

Energy=eV

E= 1.6x10^-19 x 500

E=800 x 10^-19 J

E=8 x 10^-17 J

The kinetic energy (K.E.) of photoelectrons is calculated using the energy of the incident radiation, given by the formula:

• Incident Energy (E): E = hc/λ
• Where h = Planck's constant, c = speed of light, λ = wavelength
• For energy in electron volts (eV) and wavelength in Angstroms (Å), the formula simplifies to: E = 12400/λ Å

Given:

• Wavelength, λ = 1000 Å
• E = 12400 / 1000 Å
• Therefore, E = 12.4 eV

Since the work function is negligible, the K.E. of the photoelectrons is approximately the same as the incident energy: 12.4 eV.

The electrons surrounding each atom in a semiconductor are part of a covalent bond. A covalent bond consists of two atoms "sharing" a single electron.

Each atom forms 4 covalent bonds with the 4 surrounding atoms. Therefore, between each atom and its 4 surrounding atoms, 8 electrons are being shared.

There are two types of semiconductors: p-type and n-type. Therefore both holes and electrons conduct current respectively.