Physics: CUET Mock Test - 9 - JEE MCQ

A wire bound resistor is an electrical passive component that limits current. Wire-bound resistors are made by winding the wires of an alloy like manganin on an insulating base. They are relatively insensitive to temperature.

Van de Graff generator is used to create a large amount of static electricity. A Van de Graff generator uses static electricity and a moving belt to charge a large metal sphere to a very high voltage. As the belt moves, electrons move from the rubber belt to the silicon roller, causing the belt to become positively charged and the roller to become negatively charged. As a result, it builds up positive charge.

A Van de Graff generator, by means of a moving belt and suitable brushes, transfers charge continuously to a large spherical conducting shell. As a result, a potential difference of the order of several million volts is built up and this can be used for accelerating charged particles.

Van de Graff generator was invented by Robert Jemison Van de Graff on November 28, 1933. Robert Jemison invented the Van de Graff generator, which is a kind of high-voltage electrostatic generator that accelerates particles, while he was doing his PhD in Princeton University.

A Van de Graff generators produces large voltage and less current. A Van de Graff generator is an electrostatic generator which creates very high electric potentials. It produces very high voltage direct current electricity at low current levels.

In Amplitude modulation, the modulating wave is superimposed on a high-frequency carrier wave such that the amplitude of the modulated wave varies as the amplitude of the modulating wave.

Amplitude modulation (AM) is used for broadcasting because it avoids receiver complexity. Moreover, only a diode and a capacitor are sufficient to separate the audio signal from the amplitude-modulated wave.

The modulation index for an AM wave is defined as the ratio of change in the amplitude of the carrier wave to the amplitude of the original carrier wave.

The communication channel for the transmission of a message signal that has a bandwidth of 200kHz is FM radio. AM radio is the channel required for a message signal having a bandwidth of 5 MHz. Other options are not valid.

In Amplitude modulation, the modulating wave is superimposed on a high-frequency carrier wave such that the amplitude of the modulated wave varies as the amplitude of the modulating wave. The frequency of the modulated wave is equal to the frequency of the carrier wave.

Noise is a form of amplitude variations in the transmitted signal due to several factors such as the atmosphere, industries, etc. This noise can be reduced by increasing the deviation of the frequency of the signal.

Pulse code modulation is the one preferred for digital communication. Pulse codes are used to convert an analog signal to a digital one. It is the standard form of digital audio in computers, compact discs, etc.

AGC stands for automatic gain control. Automatic gain control changes (AGC) the overall gain of a receiver automatically so that the strength of the received signal remains almost constant.

A rectifier is based on the fact that a forward bias p-n junction conducts and a reverse bias p-n junction does not conduct electricity. The rectifier is used to convert alternating current voltage (ac) to direct current voltage (dc).

For a half-wave rectifier,

r =1.21

The flow of electrons is termed electronic current. Electrons flow from the negative terminal to the positive.

Power P= V²/R​
If length reduced 10% then new resistance of filament will be R′.
R′=R−10% of R
R′=0.9R
Now new power of heater is P2​
P_2​= V²​​/R′ = V²/0.9R​​=1.1P
% increase power=11%

Potentiometer is a long wire of uniform cross section made of manganin.

• Both potentiometer and voltmeter are devices to measure potential difference.
• EMF is the terminal p.d between the electrodes of a cell in open circuit, i.e., when no current is drawn from it.
• Potentiometer measures the potential difference using null deflection method, where no current is drawn from the cell; whereas voltmeter needs a small current to show deflection.
• So, accurate measurement of p.d is done using a potentiometer.

The electrons in a conductor have random velocities and when an electric field is applied, they suffer repeated collisions and in the process move with a small average velocity, opposite to the direction of the field. This is equivalent to positive charge flowing in the direction of the field.

Potentiometer measures the potential difference using null deflection method, where no current is drawn from the cell; whereas voltmeter needs a small current to show deflection. So, accurate measurement of p.d is done using a potentiometer.

• Copper is a conductor and we know that for conductors, resistance is directly proprtional to temperature. Therefore on decreasing temperature resistance also decreases.
• Whereas, germanium is a semiconductor and for semiconductors, resistance is inversely proportional to temperature.
• So on decreasing temperature resistance increases.

If the current due to the auxillary battery is decreased, the potential gradient will be decreases, so the balancing length increases.Thus null point will move to fifth wire.

Ammeter is a device used to measure current. Since it has to allow the complete current flowing in the circuit through it, it has to be connected in series. For this reason, ammeters have very low values of resistances so that they do not add to the value of resistance connected in the circuit.

Kirchhoff's second law, also known as the Kirchhoff's voltage law (KVL) states that the sum of all voltages around a closed loop in any circuit must be equal to zero. This again is a consequence of conservation of energy.

The balance point will not change . For balancing of wheatstone bridge four arms of resistors are responsible. Interchange the position of galvanometer and cell does not affect balancing of wheatstone bridge.

According to Ohm’s law, V = IR. Therefore R= V/I

Thus, intensive recombinations of electrons and positive ions into neutral atoms and molecules occur. This results in the emission of light by the discharge, i.e., the negative glow is mainly due to a glow of recombination. Hence in electric discharge the electric current is due to both electrons and positive ions.

Current density is equal to Electric current divided by a given surface area, or it is the current flowing per a given cross section area.
The current density decreases with increase in cross section area which means they are inversely proportional.