Physics MCQs for NEET — Practice Questions with Answers

When an electromagnetic wave encounters a dielectric medium, the transmitted wave has the same frequency but different amplitude. The frequency of the wave remains unchanged because it is a property of the source of the wave. However, the amplitude changes due to the interaction of the wave with the medium, which can either absorb or reflect some of the wave's energy.

According to Maxwell, a changing electric field produces a magnetic field. This is one of the key components of Maxwell's equations, which describe how electric and magnetic fields propagate and interact. Specifically, a time-varying electric field induces a magnetic field, and vice versa.

James Clerk Maxwell was the first to predict the existence of electromagnetic waves. In 1864, Maxwell's equations showed that electric and magnetic fields could propagate through space as waves moving at the speed of light. This theoretical prediction was later experimentally confirmed by Heinrich Hertz.

If the Earth did not have an atmosphere, it would not be able to trap heat from the sun effectively. The atmosphere acts as an insulating layer that helps to retain heat. Without it, the Earth's surface would lose heat quickly, leading to a much lower temperature.

The greenhouse effect is primarily caused by the absorption and emission of infrared radiation by greenhouse gases in the Earth's atmosphere. These gases include carbon dioxide, methane, and water vapor, which trap heat and keep the planet warm.

Energy density is defined as the amount of energy stored in a given system or region of space per unit volume. The dimensional formula for energy is $ML^2T^{-2}$. Since energy density is energy per unit volume, we divide by volume, which has the dimensional formula $L^3$. Therefore, the dimensional formula of energy density is $\frac{ML^2T^{-2}}{L^3} = ML^{-1}T^{-2}$.

Carbon (C) is an insulator because the energy required to excite an electron from the valence band to the conduction band is much higher in carbon than in silicon (Si) or germanium (Ge). This means that fewer electrons are available for conduction in carbon compared to silicon and germanium.

Out of 5 valence electrons of phosphorous, 4 are shared with Si. Fifth electron can be approximated to revolve around nucleus. Situation is like H-atom $ En \approx -13.6 /n^2 ev $ for n = 1 , EN = -13.6 ev $E inside lattice = { En \over \epsilon_1^2 } = { -13.6 \over 12^2} =0.1 ev $

A P-type semiconductor is created by doping an intrinsic semiconductor with a trivalent impurity (such as boron). This leads to the creation of 'holes' which can accept electrons. However, the overall charge of the P-type semiconductor remains neutral because the number of positively charged holes is balanced by the number of negatively charged electrons.

Strong overlapping of different atomic orbitals in a solid leads to the formation of energy bands. These energy bands are crucial in determining the electrical properties of materials, such as whether they behave as conductors, semiconductors, or insulators.