Free Physics of Solids MCQs with Answers

291. Which of the following has the highest resistivity?

• A. Germanium
• B. Silver
• C. Copper
• D. Platinum

Explanation: Resistivity (ρ), is resistance R of a specimen such as a wire, multiplied by its cross-sectional area A, and divided by its length 1ρ = RA/l . The units of which are ohm.meter.The resistivity depends on the material of the conductor and the values of each element in a descending order is as follows,4.6×10-1, germanium10.6×10-8, platinum1.6×10-8, copper1.59×10-8, silverGermanium has the highest resistivity, while Silver has the least resistivity.

292. Metallic conduction involves the relatively free movement of their _ throughout the metallic lattice.

• A. Atoms
• B. Molecules
• C. Electrons
• D. Ions

Explanation: A is incorrect In metals atoms are not in combined form they are in electron pool type arrangementB is incorrect In metals molecules do not existC is correct since In metals electrons are in pool type arrangement and the can move within metal so the play their role in conductionD is incorrect because In metals ions are not present

293. The substances like germanium and silicon have:

• A. Negative temperature coefficients
• B. Positive temperature coefficients
• C. Both A and B
• D. None of the above

Explanation: Substances with a negative temperature coefficient of resistance, such as germanium and silicon, experience a decrease in resistance as temperature increases. This property is typical of semiconductors. Option A is correct. Option B describes metals, which have a positive temperature coefficient. Option C is incorrect because a material cannot simultaneously have both types of temperature coefficients. Option D is incorrect because germanium and silicon are correctly described by option A.

294. Carbon exists as allotropes, which are different crystalline or molecular forms of the same substance. Graphite and diamond are allotropes of carbon. Diamond is a non-conductor whereas graphite is a good conductor because:

• A. Graphite has a layered structure
• B. In graphite, all valence electrons are tetrahedrally bound
• C. In graphite one of valence electron is free to move
• D. Graphite is soft and greasy bound

Explanation: Graphite conducts electricity whereas diamond does not because in diamond the carbon atoms are bonded to other carbon atoms and all the valence electrons are bonded. whereas in graphite each carbon atom is only bonded to three other atoms. Therefore, there are delocalized (free) electrons in graphite due to 1 free valence electron in each carbon atom, which can move and carry a charge so graphite conducts electricity.

295. Which one of the following is the Boolean expression of the NAND gate?

• A. X = A.B
• B. B X = A + B
• C. X = Ā.B̄
• D. X = Ā + B̄

Explanation: The Boolean expression given for a NAND gate is that of logical addition and it is opposite to the AND gate The Boolean algebra for AND gate is X=A.B So, the Boolean algebra for the NAND gate is: X=A.B

296. Which one of the following is the truth table of the NAND gate?

• A. Option A
• B. Option B
• C. Option C
• D. Option D

Explanation: The NAND gate, or "NotAND" gate, is the combination of two basic logic gates, the AND gate, and the NOT gate, connected in series. The output of a NAND gate is high when either of the inputs is high or if both inputs are low. In other words, the output is always high and goes low only when both inputs are high. The logic NAND function is given by the Boolean expression X=A.B. The truth table of a NAND gate is given below

297. If signal is applied to input of non-inverting amplifier through resistance of 100kohm, and the value of feedback resistance is 10kohm, the gain is:

• A. 11
• B. 10
• C. 1.1
• D. 0.11

Explanation: The formula used for the gain in non inverting amplifier is given as: 1+(Feedback resistance/resistance of other resistor) 1+(10kohm/100kohm) 1+(0.1) 1.1 answer, this is gain.

298. In metals, why does electric conductivity decrease with the increase of temperature?

• A. Because electron movement decrease with the increase of temperature
• B. Because metal ions oscillations hinder electron movement
• C. Because electron direction changes at high temperature
• D. Because they pass heat current through collision of electrons

Explanation: The correct option is B because metal ion oscillations hinder electron movement. As temperature increases, the vibrational motion of metal ions disrupts the movement of electrons, reducing electrical conductivity in metals.

299. Crystals in general, may have grater refractive index or electrical conductivity in one direction than another. it is called:

• A. Polarity
• B. Optical activity
• C. Anisotropy
• D. Cleavage plane

Explanation: .A is incorrect since polarity is a separation of electric charge leading to a molecule or its chemical groups having an electric dipole moment, with a negatively charged end and a positively charged end. Polarity has no link to the refractive index or electrical conductivity in one direction. B is incorrect since optical activity is the ability of a substance to rotate the plane of polarization of a beam of light that is passed through it. Optical activity has no link to the refractive index or electrical conductivity in one direction. C is correct since the physical properties that depend upon the direction are called anisotropic properties and the phenomenon is referred to as anisotropy. The physical properties of crystalline solids like refractive index, coefficient of thermal expansion, and electrical and thermal conductivities are sometimes anisotropic for some crystals. The variation in these properties with direction is because the orderly arrangement of the particles in crystalline solids is different in different directions. For example, the electrical conductivity of graphite is greater in one direction than in another. D is incorrect since the plane surfaces formed by the breaking of a crystal are known as crystal cleavage planes. The angle between the adjacent cleavages of a crystal of a substance are the same but are different in the crystals of different substances. In other words, these angles are characteristics of crystalline solids. Cleavage itself is an anisotropic property but not what the question is asking for.

300. The temperature at which domains of the ferromagnetic substance disorient is:

• A. critical temperature
• B. absolute temperature
• C. Curie Temperature
• D. normal temperature

Explanation: Ferromagnetic MATERIALS can be permanently magnetized. Curie Temperature: The temperature at which the ferromagnetic element starts to lose its magnetism and becomes paramagnetic. Understanding the above-stated facts, option 'C' is the correct answer.