Physics Questions and Answers September 15, 2022

When n identical mercury droplets charged to the same potential V coalescence to form a single bigger drop. The potential of the new drop will be (b) nV (c)nV V n (d) nv

Two large parallel plates, separated by a distance of 3.0 mm have a capacitance of 10pF and are charged to a potential of 12V by a battery. The plates are disconnected of 12V by a battery. The plates are disconnected from the battery and pulled apart to 5.0 mm. The potential difference between the plates is (a) 12V (b) 20 V (c) zero (d) 7.2 V

A charge Q is placed at each of the opposite corners of a square. A charge q is placed at each of the other two corners. If the net electric force on Q is zero, then is 9 equals to D 9 (a)22 (b)1 a2 a (c) 1 B (d) 2

Use Thevenins theorem to determine the power dissipated in the 4822 resistor of the network shown in Figure 36.19. www Figure 36.19 D

Use nodal analysis to determine the current flowing in each branch of the network shown in Figure 34.18. Figure 34.18 20 Di 201 1500V 10.0

Determine the value of voltage Vxy shown in the circuit of Figure 34.17. SEV Figure 34.17 10 30 10.

For the network shown in Figure 34.16, determine the voltage V8, by using nodal analysis. 200 A Figure 34.16 10.0 4 (30 1612

The characteristic of a Zener diode is shown in Figure 13.17. Use the characteristic to determine (a) the current flowing in the diode when a reverse voltage of 30 V is applied, (b) the voltage dropped across the diode when a reverse current of 5 mA is flowing in it, (c) the voltage rating for the Zener diode, and (d) the power dissipated in the

The arms of a Wheatstone bridge ABCD have the following resistances AB R 100021.0, BC R 10020.5 CD unknown resistance R. DA Ry432.520.2. Determine the value of the unknown resistance and its accuracy of measurement. The Wheatstone bridge network is shown in Figure 12.36 and at balance Figure 12.36 De

The current flowing in a resistor R is measured by a 010A ammeter which gives an indication of 6.25 A. The voltage V across the resistor is measured by a 050 V voltmeter, which gives an indication of 36.5 V. Determine the resistance of the resistor, and its accuracy of measurement if both instruments have a limit of error of 2 of f.s.d. Neglect

The current flowing through a resistor of 5k120.4 is measured as 2.5 mA with an accuracy of measurement of 0.5. Determine the nominal value of the voltage across the resistor and its accuracy.

An amplifier has a gain of 14 dB. Its input power is 8 mW. Find its output power.

6 of the power supplied to a cable appears at the output terminals. Determine the power loss in decibels.

For the doublebeam oscilloscope displays shown in Figure 12.19, determine (a) their frequency, (b) their r.m.s. values, (c) their phase difference. The timecm switch is on 100scm and the voltscm switch on 2 Vcm. AA A. Figure 12.19

For the oscilloscope display of a pulse waveform shown in Figure 12.17 the "time/em' switch is on 50 ms/em and the 'volts/cm' switch is on 0.2 V/em. Determine (a) the periodic time, (b) the frequency. (c) the magnitude of the pulse voltage.

For the oscilloscope display of a pulse waveform shown in Figure 12.17 the timeem switch is on 50 msem and the voltscm switch is on 0.2 Vem. Determine (a) the periodic time, (b) the frequency. (c) the magnitude of the pulse voltage. Figure 12.17

For the oscilloscope square voltage waveform shown in Figure 12.16, determine (a) the periodic time, (b) the frequency and (c) the peak-to-peak voltage. The 'time/em' (or timebase control) switch is on 100s/cm and the 'volts/cm' (or signal amplitude control) switch is on 20 V/cm.

For the oscilloscope square voltage waveform shown in Figure 12.16, determine (a) the periodic time, (b) the frequency and (c) the peaktopeak voltage. The timeem (or timebase control) switch is on 100scm and the voltscm (or signal amplitude control) switch is on 20 Vcm. Figure 12.16

A current of 20 A flows through a load having a resistance of 252. Determine the power dissipated in the load. (b) A wattmeter, whose current coil has a resistance of 0.01 12, is connected as shown in Figure 12.11. Determine the wattmeter reading.

A current of 20 A flows through a load having a resistance of 252. Determine the power dissipated in the load. (b) A wattmeter, whose current coil has a resistance of 0.01 12, is connected as shown in Figure 12.11. Determine the wattmeter reading. Figure 12.11 120 A0010 A300 Supply

A coil of copper wire has a resistance of 10 52 at 20C. If the temperature coefficient of resistance of copper at 20C is 0.004/C, determine the resistance of the coil when the temperature rises to 100C.

Some copper wire has a resistance of 20012 at 20C. A current is passed through the wire and the temperature rises to 90C. Determine the resistance of the wire at 90C, correct to the nearest ohm, assuming that the temperature coefficient of resistance is 0.004/C at 0C.

Eight cells, each with an internal resistance of 0.212 and an e.m.f. of 2.2 V are connected (a) in series, (b) in parallel. Determine the e.m.f. and the internal resistance of the batteries so formed.

A cell has an internal resistance of 0.02 22 and an c.m. f. of 2.0V. Calculate its terminal p.d. if it delivers (a) 5A, (b) 50 A.

The p.d. at the terminals of a battery is 25 V when no load is connected and 24 V when a load taking 10 A is connected. Determine the internal resistance of the battery.

For the circuit shown in Figure 7.3, determine the p.d. across resistor Ry. If the total resistance of the circuit is 10012, determine the current flowing through resistor R. Find also the value of resistor R. Figure 7.3 10V 4V 25V V/

For the circuit shown in Figure 7.3, determine the p.d. across resistor Ry. If the total resistance of the circuit is 10012, determine the current flowing through resistor R. Find also the value of resistor R. Figure 7.3 10V 4V 25V V

Two resistors are connected in series across a 24V supply and a current of 3 A flows in the circuit. If one of the resistors has a resistance of 252, determine (a) the value of the other resistor, and (b) the p.d. across the 212 resistor. If the circuit is connected for 50 hours, how much energy is used?

Two resistors are connected in series across a 24V supply and a current of 3 A flows in the circuit. If one of the resistors has a resistance of 252, determine (a) the value of the other resistor, and (b) the p.d. across the 212 resistor. If the circuit is connected for 50 hours, how much energy is used

For the circuit shown in Figure 7.13, determine (a) the reading on the ammeter, and (b) the value of resistor R Figure 7.13 11 A 8A R-50 R A = 20 12 43-20

For the circuit shown in Figure 7.13, determine (a) the reading on the ammeter, and (b) the value of resistor R Figure 7.13 11 A 8A R50 R A 20 12 4320

For the circuit shown in Figure 7.15, find (a) the value of the supply voltage V and (b) the value of current I. Figure 7.15 A -60 12 2-3 A R 1 P 10 200-100

For the circuit shown in Figure 7.15, find (a) the value of the supply voltage V and (b) the value of current I. Figure 7.15 A 60 12 23 A R 1 P 10 200100

For the circuit shown in Figure 7.15, find (a) the value of the supply voltage V and (b) the value of current I. Figure 7.15 A 60 12 23 A R 1 P 10 200100

Determine the Thvenin equivalent circuit with respect to terminals AB of the circuit shown in Figure 36.32. Hence determine (a) the magnitude of the current flowing in a (3.75+j11) 2 impedance connected across terminals 4B, and (b) the magnitude of the p.d. across the (3.75+/11) impedance Figure 36.32 30 30 E

Determine the Thvenin equivalent circuit with respect to terminals AB of the circuit shown in Figure 36.32. Hence determine (a) the magnitude of the current flowing in a (3.75j11) 2 impedance connected across terminals 4B, and (b) the magnitude of the p.d. across the (3.7511) impedance Figure 36.32 30 30 E

when the current in the primary coil of 1000 turns increases linearly from 1 A to 6A in 200 ms, an em.f. of 15V is induced into the secondary coil of 480 turns, which is left open circuited. Determine (a) the mutual inductance of the two coils, (b) the reluctance of the former and (c) the self inductance of the primary coil. 1000 m Figure 11.12

In the device shown in Figure 11.12. when the current in the primary coil of 1000 turns increases linearly from 1 A to 6A in 200 ms, an em.f. of 15V is induced into the secondary coil of 480 turns, which is left open circuited. Determine (a) the mutual inductance of the two coils, (b) the reluctance of the former and (c) the self inductance of the

The wing span of a metal aeroplane is 36m. If the aeroplane is flying at 400 kmh, determine the e.m.f. induced between its wing tips. Assume the vertical component of the earths magnetic field is 40.T.

A conductor moves with a velocity of 15ms at an angle of (a) 90, (b) 60 and (c) 30 to a magnetic field produced between two squarefaced poles of side length 2 cm. If the flux leaving a pole face is 5uWb, find the magnitude of the induced e m.f. in each case.

A conductor 300 mm long moves at a uniform speed of 4 m/s at right-angles to a uniform magnetic field of flux density 1.25 T. Determine the current flowing in the conductor when (a) its ends are open-circuited, (b) its ends are connected to a load of 2012 resistance.

A conductor 300 mm long moves at a uniform speed of 4 ms at rightangles to a uniform magnetic field of flux density 1.25 T. Determine the current flowing in the conductor when (a) its ends are opencircuited, (b) its ends are connected to a load of 2012 resistance.

A conductor 350mm long carries a current of 10 A and is at right-angles to a magnetic field lying between two circular pole faces each of radius 60 mm. If the total flux between the pole faces is 0.5 mWb, calculate the magnitude of the force exerted on the conductor.

A conductor 350mm long carries a current of 10 A and is at rightangles to a magnetic field lying between two circular pole faces each of radius 60 mm. If the total flux between the pole faces is 0.5 mWb, calculate the magnitude of the force exerted on the conductor.

A mild steel ring has a radius of 50 mm and a crosssectional area of 400 mm. A current of 0.5 A flows in a coil wound uniformly around the ring and the flux produced is 0.1 mWb. If the relative permeability at this value of current is 200, find (a) the reluctance of the mild steel and (b) the number of turns on the coil.

A coil of 300 turns is wound uniformly on a ring of nonmagnetic material. The ring has a mean circumference of 40 cm and a uniform crosssectional area of 4 cm. If the current in the coil is 5 A, calculate (a) the magnetic field strength, (b) the flux density and (c) the total magnetic flux in the ring

A magnetizing force of 8000 Am is applied to a circular magnetic circuit of mean diameter 30 cm by passing a current through a coil wound on the circuit. If the coil is uniformly wound around the circuit and has 750 turns, find the current in the coil.

The maximum working flux density of a lifting electromagnet is 1.8 T and the effective area of a pole face is circular in crosssection. If the total magnetic flux produced is 353 mWb, determine the radius of the pole face.

A magnetic pole face has a rectangular section having dimensions 200 mm by 100 mm. If the total flux emerging from the pole is 150u. Wb, calculate the flux density.

A capacitor is charged with 10mC. If the energy stored is 1.21, find (a) the voltage and (b) the capacitance.

Determine the energy stored in a 3 F capacitor when charged to 400 V. (b) Find also the average power developed if this energy is dissipated in a time of 10s.

A capacitor is to be constructed so that its capacitance is 0.2 F and to take a p.d. of 1.25 kV across its terminals. The dielectric is to be mica which, after allowing a safety factor of 2, has a dielectric strength of 50MVm. Find (a) the thickness of the mica needed, and (b) the area of a plate assuming a twoplate construction. (Assume E, for

Capacitances of 3 F, 6F and 12F are connected in series across a 350V supply. Calculate (a) the equivalent circuit capacitance, (b) the charge on each capacitor and (c) the p.d. across each capacitor. The circuit diagram is shown in Figure 8.9. C3F CF C12 F HH HH Figure 8.9 V V V350 V

The flux density between two plates separated by mica of relative permittivity 5 is 2 Cm Find the voltage gradient between the plates.

Two parallel rectangular plates measuring 20 cm by 40cm carry an electric charge of 0.2 C. Calculate the electric flux density. If the plates are spaced 5 mm apart and the voltage between them is 0.25 kV, determine the electric field strength

A 5F capacitor is charged so that the p.d. between its plates is 800 V. Calculate how long the capacitor can provide an average discharge current of 2 mA.

A direct current of 4 A flows into a previously uncharged 20F capacitor for 3 ms. Determine the p.d. between the plates.

Three identical lamps A, B and C, are connected in series across a 150 V supply. State (a) the voltage across each lamp, and (b) the effect of lamp C failing.

Calculate the volt drop across the 60 22 load in the circuit shown in Figure 7.36 when the slider S is at the halfway point of the 2002 potentiometer. Figure 7.36 30V 2001 S 6011 B

Given four 12 resistors, state how they must be connected to give an overall resistance of (a) 42 (b) 1 2 (c) 14 12 (d) 2412, all four resistors being connected in each case.

Calculate the crosssectional area, in mm, of a piece of copper wire, 40 m in length and having a resistance of 0.25 12. Take the resistivity of copper as 0.02 x 10 m.

Calculate the crosssectional area, in mm, of a piece of copper wire, 40 m in length and having a resistance of 0.25 12. Take the resistivity of copper as 0.02 x 10 m.

Problem 1. The resistance of a 5 m length of wire is 60012. Determine (a) the resistance of an 8m length of the same wire, and (b) the length of the same wire when the resistance is 42012

The hot resistance of a 240 V filament lamp is 9602. Find the current taken by the lamp and its power rating.

The hot resistance of a 240 V filament lamp is 9602. Find the current taken by the lamp and its power rating.

Calculate the power dissipated when a current of 4 mA flows through a resistance of 5 km2.

Calculate the power dissipated when a current of 4 mA flows through a resistance of 5 km2.

A current of 5 A flows in the winding of an electric motor, the resistance of the winding being 10052. Determine (a) the p.d. across the winding, and (b) the power dissipated by the coil.

A current of 5 A flows in the winding of an electric motor, the resistance of the winding being 10052. Determine (a) the p.d. across the winding, and (b) the power dissipated by the coil.

The current/voltage relationship for two resistors A and B is as shown in Figure 4.5. Determine the value of the resistance of each resistor Figure 4.5 Current/mA 8 15 10 10 O Resistor B 8 12 16 20 Voltage V

The currentvoltage relationship for two resistors A and B is as shown in Figure 4.5. Determine the value of the resistance of each resistor Figure 4.5 CurrentmA 8 15 10 10 O Resistor B 8 12 16 20 Voltage V

A d.c. source has an opencircuit voltage of 30 V and an internal resistance of 1.502. State the value of load resistance that gives maximum power dissipation and determine the value of this power.

A field effect transistor operates with a drain current of 100 mA and a gate-source bias of -IV. The device has a ga value of 0.25. If the bias voltage decreases to -1.1 V, determine (a) the change in drain current and (b) the new value of drain current.

A field effect transistor operates with a drain current of 100 mA and a gatesource bias of IV. The device has a ga value of 0.25. If the bias voltage decreases to 1.1 V, determine (a) the change in drain current and (b) the new value of drain current.

Figure 14.21 shows the mutual characteristic for a junction gate field effect transistor. When the gatesource voltage is 2.5 V, determine (a) the value of drain current, (b) the dynamic value of forward transconductance. 25V Figure 14.21 12 MA 4 5 mA 2.5 V 5.0 4.5 4.0 3.5 3.0 2.5 2.0 1.5 1.0 0.5 Gatesource voltage. Vos (V) 20 18 16 14 12 10 P 4 N

A bipolar transistor has a common-emitter current gain of 125. If the transistor operates with a collector current of 50 mA, determine the value of base current.

Figure 14.15 shows the output characteristic for an npn silicon transistor. When the collectoremitter voltage is 10 V and the base current is 80 A, determine (a) the value of collector current, (b) the static value of output resistance and (c) the dynamic value of output resistance. Collector current (MA) 20 TH 10 14 301 1010mA1BmA Figure 14.15

Explain briefly the terms given below when they are associated with a p-n junction: (a) conduction in intrinsic semiconductors, (b) majority and minority carriers, and (c) diffusion.

Explain briefly why a junction between p-type and n-type materials creates a contact potential.

Sketch the forward and reverse characteristics of a silicon p-n junction diode and describe the shapes of the characteristics drawn.

If momentum [P], area [A] and time [T] are taken as fundamental quantities, then the dimensional formula for the coefficient of viscosity is (A) [PA 1 T 0 ] (B) [PAT 1 ] (C) [PA 1 T] (D) [PA 1 T 1 ]

Following statements are given: (A) The average kinetic energy of a gas molecule decreases when the temperature is reduced. (B) The average kinetic energy of a gas molecule increases with increase in pressure at constant temperature. (C) The average kinetic energy of a gas molecule decreases with increase in volume. (D) Pressure of a gas increases

Which of the following statement is correct? (A) In primary rainbow, observer sees red colour on the top and violet on the bottom (B) In primary rainbow, observer sees violet colour on the top and red on the bottom (C) In primary rainbow, light wave suffers total internal reflection twice before coming out of water drops (D) Primary rainbow is

Time taken by light to travel in two different materials A and B of refractive indices ? A and ? B of same thickness is t 1 and t 2 respectively. If t 2 t 1 = 5 10 10 s and the ratio of ? A to ? B is 1 : 2. Then, the thickness of material, in meter is: (Given v A and v B are velocities of light in A and B materials, respectively.) (A) 5 10 -10

A 63.0kg sprinter starts a race with an acceleration of 4.20 ms. What is the net external force on him

Obtain the sine series for unity in (0,7).

300.0 calories are used to raise the temperature of a 50.0 g block of iron. If the initial temperature of the iron is 103 o C , what is its final temperature? (Hint: ?T=242 o C).

A body of mass 5 kg is placed at the origin, and can move only on the xaxis. A force of 10N is acting on it in a direction making an angle of 60 with the xaxis and displaces it along the xaxis by 4 metres. The work done by the force is (a) 2.5J (b) 7.25 J (c) 40 J (d) 20 J 6

A force F (53) N is applied over a particle which displaces it from its origin to the point r (21) metres. The work done on the particle is (a)7J (b) 13J (c)7J (d) 11 J

The workenergy theorem states that the change in (a) kinetic energy of a particle is equal to the work done on it by the net force. (b) kinetic energy of a particle is equal to the work done by one of the forces acting on it. (c) potential energy of a particle is equal to the work done on it by the net force. (d) potential energy of a particle is

A horizontal force of 5N is required to maintain a velocity of 2 ms for a block of 10kg mass sliding over a rough surface. The work done by this force in one minute is (a) 600J (b) 60 J (c) 6 J (d) 6000 J

An object of mass m is released from rest from the top of a smooth inclined plane of height h. Its speed at the bottom of the plane is proportional to (a) m (b) m (c) m (d) m

A 10kg satellite completes one revolution around the earth at a height of 100 km in 108 minutes. The work done by the gravitational force of earth will be (a) 108 100 10J 10010 108 (c) J 108x10 100 (b) (d) zero J

A raindrop of mass 1 g falling from a height of 1km hits the ground with a speed of 50 ms . If the resistive force is proportional to the speed of the drop, then the work done by the resistive force is (Take g 10 ms ) (a) 10J (b) 10 J (c) 8.75 J (d)8.75 J

A position dependent force F(72x3x) N acts on a small abject of mass 2kg to displace it from x 0 and .x 5m. The work done in joule is (a) 70J (b) 270 J (c) 35 J (d) 135 J

A weightlifter lifts a weight off the ground and holds it up (a) work is done in lifting as well as holding the weight. (b) no work is done in both lifting and holding the weight (c) work is done in lifting the weight but no work is required to done in holding it up. (d) no work is done in lifting the weight but work is required to be done in

A particle moves under the effect of a force F Cx from x 0 to x x. The work done in the process is (a) Cx (d) zero 1 (b) Cx (c) Cx

The vessels A and B of equal volume and weight are immersed in water to a depth h. The vessel A has an opening at the bottom through which water can enter. If the work done in immersing A and B are Wand WB respectively, then (a) W W B (c) W W B (b) W

A body of mass 4 kg is moving with momentum of 8 kg ms . A force of 0.2N acts on it in the direction of motion of the body for 10s. The increase in kinetic energy is (a) 10 J (b) 8.5J (c) 4.5 J (d) 4 J

Work done in time t on a body of mass m which is accel erated from rest to a speed v in time t, as a function of time t is given by 1 (a)m my (1) 12 (b) m 1 1 v (4) m

A 10kg mass moves along xaxis. Its acceleration as a function of its position is shown in the figure. What is the total work done on the mass by the force as the mass moves from x0 tox8cm. (a) 8 10 J (c) 4 10 J a (cmsec) 154 10 5 0 2 4 6 8 x (cm) (b) 16 10 J (d) 1.6 10J

A body is being raised to a heighth from the surface of earth. What is the sign of work done by applied force and gravitational force respectively (a) Positive, Positive (b) Positive, Negative (d) Negative, (c) Negative, Positive

The relationship between force and position is shown in the figure given (in one dimensional case). The work done by the force in displacing a body from.x 1cm to x 5 cm is Force 20 0 10 20 123456 x (cm) (a) 20 ergs (b) 60 ergs (c) 70 ergs (d) 700 ergs

The work done by a body against friction always result in (a) loss of kinetic energy (b) loss of potential energy (c) gain of kinetic energy (d) gain of potential energy

The graph between the resistive force F acting on a body and the distance covered by the body is shown in the figure. The mass of the body is 25kg initial velocity is 2 ms. When the distance covered by the body is 5m, its kinetic energy would be (a) 50 J 20 10 0 1 2 3 4 x (m) (c) 20 J (b) 40 J (d) 10 J

Which of the following statements is incorrect (a) Kinetic energy may be zero, positive or negative. (b) Power, energy and work are all scalars. (c) Potential energy may be zero, positive or negative. (d) Ballistic pendulum is a device for measuring the speed of bullets.

If W, W and W, represent the work done in moving a particle from A to B along three different paths 1, 2 and 3 respectively (as shown) in the gravitational field of a point mass m, find the correct relation (a) W W W 1 2 3 (c) W W 2

If the force acting on a body is inversely proportional to its speed, then its kinetic energy is (a) linearly related to time (b) inversely proportional to time (c) inversely proportional (d) a constant to the square of time

A particle of mass 0.01kg travels along a curve with velocity given by 4 16 ms. After some time, its velocity becomes 8720 jms due to the action of a,conservative force. The work done on particle during this interval of time is (a) 0.32J (b) 6.9 J (c) 9.6J (d) 0.96 J

A truck and a car moving with the same kinetic energy are brought to rest by the application of brakes which provide equal retarding forces. Which of them will come to rest in a shorter distance (a) The truck (b) The car (c) Both will travel the same distance before coming to rest (d) Cannot be predicted

A particle of mass m and charge q is accelerated through a potential difference of V volt. Its energy is (a) qV (b) mqV (c) 9 m (d) 9 mV

An ice cream has a marked value of 700 kcal. How many kilowatt hour of energy will it deliver to the body as it is digested. (a) 0.81 kWh (c) 1.11 kWh (b) 0.90 kWh (d) 0.71 kWh

Consider the following two statements 1. Linear momentum of a system of particles is zero 2. Kinetic energy of a system of particles is zero Then, (a) 1 implies 2 and 2 implies 1 (b) 1 does not imply 2 and 2 does not imply (c) 1 implies 2 but 2 does not imply 1 (d) 1 does not imply 2 but 2 implies 1

In the nonrelativistic regime, if the momentum, is increased by 100, the percentage increase in kinetic energy is (a) 100 (b) 200 (c) 300 (d) 400

A running man has half the kinetic energy of that of a boy of half of his mass. The man speeds up by 1 ms so as to have same K.E. as that of boy. The original speed of the man will be (a) 2 ms 1 (21) (c) ms (b)(21) ms 1 (d) ms

A body of mass 10kg at rest is acted upon simultaneously by two forces 4N and 3N at right angles to each other. The kinetic energy of the body at the end of 10 sec is (a) 100 J (b) 300 J (c) 50 J (d) 125 J