12th Grade Physics Practice Paper!

A Zener diode is a semiconductor device that operates under reverse bias conditions. When a Zener diode is reverse biased, it allows current to flow in the reverse direction once a certain voltage threshold, known as the Zener voltage, is reached. This characteristic makes Zener diodes useful for voltage regulation and protection against voltage spikes. Unlike other semiconductor devices listed, such as solar cells, transistors, and microprocessors, which operate under forward bias conditions, the Zener diode specifically functions under reverse bias.

A galvanometer is a device used to measure the flow of electric current in a circuit. It consists of a coil of wire suspended in a magnetic field. When current flows through the coil, it creates a magnetic field that interacts with the external magnetic field, causing the coil to rotate. By measuring the angle of rotation, the current can be determined. Unlike other options like voltmeter, Wheatstone Bridge, and potentiometer, a galvanometer is specifically designed to measure the flow of current and not other electrical quantities like voltage or resistance. Therefore, a galvanometer is the correct answer for a device used only to check the flow of current in a circuit.

When a copper plate oscillates between two magnetic poles, the movement of the plate induces a current in the plate known as eddy current. These eddy currents create their own magnetic fields that oppose the motion of the plate, resulting in damping. Therefore, the reason for the damping of the copper plate in this scenario is eddy currents.

The condition for maximum power dissipation occurs when the load resistance is equal to the internal resistance of the source. This is because maximum power is transferred from the source to the load when the load resistance matches the internal resistance, resulting in maximum power dissipation. If the load resistance is higher or lower than the internal resistance, the power dissipation will be less than the maximum value.

When a bridge is balanced, it means that the ratio of the resistances in the arms of the bridge is such that there is no potential difference across the galvanometer. In other words, the potential difference across the galvanometer is zero, resulting in no deflection. This occurs when the bridge is adjusted in such a way that the ratio of the resistances in the arms of the bridge is equal to the ratio of the resistances in the other arms.

Below the threshold frequency, no emission of photoelectrons occurs. This is because the threshold frequency is the minimum frequency of incident light required to eject electrons from a metal surface. If the frequency of the incident light is below the threshold frequency, the energy of the photons is not sufficient to overcome the binding energy of the electrons in the metal, and therefore no photoelectrons are emitted.

The current enclosed by the toroid will be zero because there are no conducting loops or paths for the current to flow through. Since the charge is placed at the center of the toroid, it does not create any magnetic field lines that would induce a current in the toroid. Therefore, there is no current enclosed by the toroid.

Drift velocity refers to the average velocity at which electrons move in a conductor when they are subjected to an electric field. It is independent of time because although the electrons are constantly being accelerated by the electric field, they also experience frequent collisions with atoms in the conductor, which randomize their individual velocities. As a result, the average velocity of the electrons remains constant over time, leading to the phenomenon of drift velocity.

When a dielectric medium is introduced in between a capacitor, the capacitance increases. This is because the dielectric material reduces the electric field between the plates of the capacitor, which in turn increases the capacitance. The dielectric material increases the ability of the capacitor to store electric charge, thereby increasing the capacitance.

The equation A+B = Y represents the logical operation of OR gate. In an OR gate, the output is true if either of the inputs A or B is true, or if both are true. The equation A+B = Y indicates that the output Y is true when either A or B or both are true, which aligns with the behavior of an OR gate. Therefore, the correct answer is OR Gate.

When the distance between the coils is increased, the mutual inductance of both coils decreases. This is because mutual inductance is directly proportional to the coupling between the coils, which is influenced by their proximity. As the distance between the coils increases, the magnetic field generated by one coil has less effect on the other coil, resulting in a decrease in mutual inductance.

The correct answer is Becquerel. The SI unit of radioactivity is the Becquerel (Bq), which measures the rate of radioactive decay. It is named after Henri Becquerel, a French physicist who discovered radioactivity. The Becquerel is defined as one radioactive decay event per second. This unit is used to quantify the amount of radioactive material and is commonly used in fields such as nuclear physics, medicine, and environmental science.

An equipotential surface is a surface in which all points have the same electric potential. This means that the electric field is perpendicular to the surface at every point. Since no work is done to move a test charge along an equipotential surface, it implies that the electric field is zero along the surface. Therefore, the correct answer is "No work is done to bring a test charge to a near charge."

Electric dipole moment is a vector quantity because it has both magnitude and direction. It is defined as the product of the magnitude of the charge and the distance between the charges in an electric dipole, multiplied by the direction from the negative charge to the positive charge. This means that the electric dipole moment has both a numerical value and a specific direction, making it a vector quantity.

A telescope has a small eyepiece and a large objective lens. The objective lens is responsible for gathering and focusing light from distant objects, while the eyepiece magnifies the image created by the objective lens. The large objective lens allows for a greater amount of light to enter the telescope, resulting in a brighter and clearer image. The small eyepiece is used to magnify the image further for the viewer. Therefore, a telescope is the correct answer in this case.

Endoscopy is a medical procedure that involves inserting a long, flexible tube with a camera at the end into the body to visualize internal organs or structures. Total Internal Reflection (TIR) is the principle on which endoscopy is based. TIR occurs when light traveling in a medium with a higher refractive index encounters a boundary with a medium of lower refractive index at an angle greater than the critical angle. This causes the light to be completely reflected back into the higher refractive index medium, allowing for the visualization of internal structures without the need for invasive surgery.

A converging lens is used to converge the light beam at a single point on the screen during diffraction. This is because a converging lens has a convex shape that causes the light rays to bend towards each other, ultimately focusing them to a single point. This property of the converging lens allows for the formation of a clear and focused image on the screen during diffraction.

Kirchhoff's Junction Rule is based on the conservation of charge. It states that the total current entering a junction in an electrical circuit is equal to the total current leaving the junction. This principle is derived from the law of conservation of charge, which states that charge cannot be created or destroyed, only transferred or redistributed. Therefore, Kirchhoff's Junction Rule is a direct application of the conservation of charge principle in electrical circuits.

Welders wear special goggles to protect their eyes from ultraviolet rays because welding produces intense light and heat, which can emit harmful UV radiation. Prolonged exposure to UV rays can cause damage to the eyes, including photokeratitis (similar to sunburn of the eyes), cataracts, and even permanent vision loss. Therefore, wearing goggles with UV protection is essential for welders to safeguard their eyes from these harmful rays and prevent long-term eye damage.

Linearly polarized light only vibrates in one plane. This means that the electric field vector of the light waves oscillates in a single direction as the waves propagate. This is in contrast to unpolarized light, which vibrates in all possible directions perpendicular to the direction of propagation. The polarization of light can be achieved through various methods such as passing it through a polarizing filter or reflecting it at a specific angle.

Increasing the number of spokes in a wheel does not affect the emf induced between the axle and the rim. The emf induced in a wheel is determined by the rate of change of magnetic flux passing through the area enclosed by the wheel. The number of spokes does not affect the magnetic flux or the rate of change of magnetic flux, so the emf remains unchanged.

Voltage has a magnitude but not a direction. Voltage, also known as electric potential difference, represents the electric potential energy per unit charge in an electrical circuit. It is a scalar quantity, meaning it has magnitude but no specific direction. In contrast, the other options have both magnitude and direction:

The electric flux due to the charges would be 0 because the net electric flux through a closed surface is equal to the net charge enclosed by that surface divided by the electric constant. In this case, the charges are located at the origin and at a distance of 4b from the origin, both outside the Gaussian sphere. Therefore, there is no charge enclosed by the Gaussian sphere, resulting in a net electric flux of 0.

The resistance of a light bulb can be calculated using Ohm's Law, which states that resistance is equal to voltage divided by current. In this case, the power rating of the light bulb is given as 100 W and the supply voltage is 220 V. Using the formula P = V^2 / R, we can rearrange it to solve for resistance. Rearranging the formula gives R = V^2 / P. Plugging in the values, we get R = (220^2) / 100 = 484 Ω. Therefore, the resistance of the light bulb would be 484 Ω.

The direction of the flow of current in a wire CD parallel to AB would be West to East. This is because current flows in the opposite direction of the flow of electrons. Since the current in wire AB is flowing from east to west, the electrons in wire CD would be flowing from west to east, resulting in a current flow in the same direction.

The Paschen series refers to a set of spectral lines in the emission spectrum of hydrogen. These lines are produced when an electron transitions from a higher energy level to the third energy level (n=3). The energy difference between these levels corresponds to infrared light. Therefore, the Paschen series lies in the infrared region of the electromagnetic spectrum.

The correct answer is "Low potential to high potential" because drift velocity refers to the net velocity of charged particles, such as electrons, in a particular direction due to an electric field. In this case, the electrons move from a region of low electric potential (low potential) to a region of high electric potential (high potential). This movement is in the direction opposite to the electric field, as electrons are negatively charged particles.

When a Polaroid is rotated, it acts as a polarizing filter that only allows light waves oscillating in a specific direction to pass through. As the Polaroid is rotated, the alignment of the polarizing molecules changes, causing a decrease in the intensity of transmitted light. This decrease in intensity occurs because only a portion of the light waves align with the new orientation of the Polaroid, while the rest are blocked. Therefore, the intensity of transmitted light becomes half when the Polaroid is rotated.

A transistor acts as a switch when the collector current is zero. In this state, the transistor is turned off and does not allow current to flow through it. This is because the base-emitter junction is not forward biased, preventing the transistor from conducting. By keeping the collector current at zero, the transistor effectively acts as an open switch, allowing for control of current flow in a circuit.

A negative resistance can be found during a negative slope in a semiconductor. This means that as the voltage increases, the current decreases, which is opposite to the normal behavior of a resistor. In a negative slope, the semiconductor exhibits a decrease in resistance with increasing voltage, resulting in a negative resistance. This behavior can occur in certain types of semiconductors, such as tunnel diodes or Gunn diodes, where the negative resistance region is utilized for specific applications like oscillators or amplifiers.

The Square Law Device is classified as a non-linear device because it does not exhibit a linear relationship between the input and output signals. In other words, the output of the device is not directly proportional to the input. Instead, the output signal is a function of the square of the input signal. This non-linear behavior makes the Square Law Device useful in various applications such as signal processing, modulation, and amplification, where non-linear effects are desired or required.

If an open circuit is used in place of the closed loop, flux will be induced across the open ends of the circuit. In an open circuit, there is a break in the path for the current to flow, so when there is a change in magnetic field, it will induce a voltage across the open ends of the circuit. This induced voltage can cause a current to flow momentarily, creating a flux across the open ends of the circuit.

The visibility of De Broglie waves associated with an object is not determined by its mass. De Broglie waves are a wave-particle duality concept in quantum mechanics, where all particles, including macroscopic objects like footballs, exhibit wave-like properties. The visibility of these waves is determined by the wavelength of the associated wave, which is inversely proportional to the momentum of the object. Therefore, the correct answer is that the mass of the football does not affect the visibility of its De Broglie waves.

Ultrasonic waves will not show polarization because they are mechanical waves that require a medium to propagate, such as solids, liquids, or gasses. Unlike electromagnetic waves (such as light, microwaves, and radio waves), which are transverse waves and can exhibit polarization, ultrasonic waves are longitudinal waves. This means that the vibrations of particles in the medium are parallel to the direction of wave propagation, making polarization impossible.

Fusion is the correct answer because it is the process by which the sun and stars produce energy. Fusion occurs when two or more atomic nuclei come together to form a heavier nucleus, releasing a large amount of energy in the process. This is the opposite of fission, which involves the splitting of atomic nuclei. Photon energy refers to the energy carried by photons, which are particles of light, but it is not the source of energy in the sun and stars. Combustion is a chemical reaction that releases energy, but it is not the process that powers the sun and stars.

When an accelerating electron revolves around the nucleus, according to Bohr, a continuous spectrum would be emitted. This means that a range of wavelengths and frequencies would be present in the emitted light. Continuous spectra are typically observed when a heated solid or a dense gas emits light, as opposed to discrete lines or bands of specific wavelengths seen in line or zigzag spectra.

The displacement current in a capacitor is equal to the rate of change of electric flux through the capacitor. In this case, since the capacitor is being charged by an external AC source with an instantaneous current of I0 cos ωt, the electric flux through the capacitor will be changing with time. Therefore, there will be a displacement current flowing through the capacitor.

A potentiometer is not affected by the internal resistance of the source because it draws no current from the voltage source being measured. This means that the potentiometer does not create any additional load on the source, allowing it to accurately measure the voltage without affecting the internal resistance.

The proton will exit the cyclotron first because it is the lightest particle among the given options. In a cyclotron, charged particles are accelerated by a magnetic field and an alternating electric field. The acceleration depends on the mass of the particle and the strength of the magnetic field. Since the proton has the smallest mass compared to the other options, it will experience a greater acceleration and exit the cyclotron first.

The decay of a light bulb can be compared to radioactive decay because both processes involve the gradual decrease in intensity or activity over time. In radioactive decay, unstable atomic nuclei emit radiation and transform into more stable forms, while in the decay of a light bulb, the filament gradually loses its ability to emit light and eventually fails. Both processes follow a similar pattern of decline and can be described as a decay phenomenon.

The current through the resistance connected to three voltage sources connected in parallel will be the sum of the currents from each individual voltage source. In a parallel circuit, the voltage across each component is the same, but the current splits between the components. Therefore, the current through the resistance will be the sum of the currents from each voltage source.

Magnetic declination refers to the angle between the true geographic north and the magnetic north. It represents the difference between the direction indicated by a compass and the actual direction of true north. This angle can vary depending on the location on Earth and changes over time due to the movement of the Earth's magnetic field. Magnetic declination is an important concept for navigation and is used to correct compass readings to obtain accurate directions.

When light passes through a medium with different refractive indices, such as from water to air, it changes direction. In the case of an air bubble inside water, the light rays bend away from the normal, causing the bubble to act as a diverging or concave lens. This type of lens causes light rays to spread out, resulting in a virtual and diminished image.

Space waves are used for line of sight communication. Line of sight communication refers to the transmission of signals in a straight line without any obstacles. Space waves, also known as terrestrial waves, propagate in a straight line and do not require any reflection or refraction to reach the receiver. They are commonly used for communication between two points that are within the direct line of sight of each other, such as in point-to-point microwave links or satellite communication systems.

Iron has a high binding energy compared to the other elements listed. This is because iron has a higher number of protons and neutrons in its nucleus, resulting in a strong nuclear force of attraction holding the nucleus together. The strong binding energy of iron makes it more stable and less likely to undergo nuclear reactions or decay.

Neutrino detection is difficult because neutrinos have weak interaction with other particles. This means that they rarely interact with matter, making it challenging to detect them. Neutrinos can pass through large amounts of material without being absorbed or scattered, making their detection a complex task.

The centripetal force is dynamically stable in a hydrogen atom because it is responsible for keeping the electron in orbit around the nucleus. It acts as a center-seeking force, constantly pulling the electron towards the nucleus, preventing it from flying off in a straight line. This force is necessary to maintain the stability of the atom's structure and ensure that the electron remains in its designated energy level. Without the centripetal force, the electron would move in a straight line and the atom would become unstable.

The S.I. unit for current sensitivity is (Ampere)-1. This means that the unit is the reciprocal of the ampere, which is the unit of electric current. The negative exponent indicates that it is the inverse of the ampere. Current sensitivity refers to the ability of a device or instrument to detect or measure small changes in current. Therefore, the unit for current sensitivity is the inverse of the ampere, indicating that it measures the sensitivity of a device to changes in current.

Gauss' Law depends on the Inverse Square Law. Gauss Law states that the electric flux through a closed surface is directly proportional to the charge enclosed by that surface. The Inverse Square Law states that the intensity of a physical quantity decreases as the distance from the source increases, following an inverse square relationship. In the case of Gauss Law, the electric flux decreases as the distance from the charge source increases, in accordance with the Inverse Square Law. Therefore, Gauss Law depends on the Inverse Square Law.

Avalanche breakdown occurs at the critical voltage in a diode. During avalanche breakdown, the electric field across the diode becomes so high that it causes the collision of electrons with atoms in the crystal lattice, creating more free electrons and holes. This process leads to a rapid increase in the current flowing through the diode, causing it to break down and conduct in the reverse direction.