Electronics Physics Quiz | objective questions | Physics General Knowledge Questions | MCQ

Electronics Physics Quiz | objective questions | Physics General Knowledge Questions | MCQ

1 >>which of the following methods can be used to charge a metal sphere positively without touching it . Select the best ?

• (A) Rub it with a piece of fur
• (B) Rub it with a piece of silk
• (C) Bring a negatively charged rod near the sphere and touch it to ground for a short while
• (D) Connect the positive terminal a battery and float the other end of the battery

Solution This can be possible by induction, if a negative charge rod is placed near the sphere (at a distance not in touch) than it attract positive charge inside the sphere towards its side and the negative charges collected on other side and when the negative surface connected to earth than the negative charge goes to earth and the sphere remain positively charged.

2 >>If 10⁹ electrons move out of a body to another body every second, how much time is approximately required to get a total charge of 1 C on the other body? ?

• (A) 180 years
• (B) 220 years
• (C) 200 years
• (D) 120 years

Solution Total charge transferred per second q=ne=109×1.6×10-19=1.6×10-10C. So 1.6×10-10C charge transferred in time=1second

3 >>Electric charge ?

• (A) is a property of neutrons onlz
• (B) is a property of electrons only
• (C) is a property of protons only
• (D) is a property of particles such as atoms,ions,electrons etc that defines their behaviour in electrical fields.

Solution If +Q is at point P, another charge +q is placed near it than +q experience repulsion while –q experience attraction so the nature of charge q can be defined by the field or force exerted by charge +Q .

4 >>Electric charges are of ?

• (A) 4 types
• (B) 2 types
• (C) 3 types
• (D) 5 types

Solution Two types (1) positive charge—deficiency of electrons i.e. if a body loses electrons it will be positive. (1) negative charge—excess of electrons i.e. if a body gains electrons it will be positive

5 >>Conservation of charges in tribo electric charging ?

• (A) implies half are positively charged and other half are neutral
• (B) implies both are positively charged
• (C) implies one is positively charged and the other is negatively charged.
• (D) implies both are negatively charged

Solution If a glass rod is rubbed with silk it becomes positive and silk gains same amount of negative charge so the total charge before and after the reaction is same so charge never be created nor be destroyed but transferred from one body to other.

6 >>Two positive charges ?

• (A) attract each other
• (B) repel each other
• (C) always attract each other
• (D) attract each other at times and repel at other times

Solution Unlike charges attract while like charges repel each other so between two positive charges repulsion is working.

7 >>Charge is quantized means ?

• (A) charges can take on discrete values that are multiples of charge on electron
• (B) charges can take on discrete values that are multiples of charge on neutron
• (C) charges can take on any continuous value
• (D) charges can take on any discontinuous value

Solution Total charge transferred from one body to other can be calculated by the number of electrons it is known as quantisation of charge given by q=±ne, where n= number of electrons , which should be an integer.

8 >>Ionization of a neutral atom is the ?

• (A) only gain of one or more electrons
• (B) only gain of one or more neutrons
• (C) only gain of one or more protons
• (D) gain or loss of one or more electrons

Solution It is not possible to remove or add protons to atom, but electron can be added or removed by an atom easily so charge can be developed on an atom removing or adding electrons , by adding becomes negative ,by removing becomes positive.

9 >>electrostatic force is ?

• (A) force exerted by an electron on a neutron
• (B) force exerted by one charge on another when the two are moving in a given frame of reference
• (C) force exerted by one charge on another when the two are at rest in a given frame of reference
• (D) force exerted by one charge on another when the two are accelerating in a given frame of reference

Solution Electrostatics means charges at rest ,or relatively at rest so this force can be applicable only when charge produce electric field which is constant which is possible only when charges at rest or relatively at rest.

10 >>Conductors are materials ?

• (A) that allow movement of electrons
• (B) that allow only random movement of electrons
• (C) that allow movement of neutrons
• (D) that allow movement of protons

Solution In conductors some electrons are unpaired so these electrons can move freely.

11 >>In charging by Induction ?

• (A) a metallic object is charged by rubbing it with fur
• (B) a metallic object by touching touching with a charged object
• (C) a metallic object is charged by bringing a charged object near it
• (D) a metallic object is charged by rubbing it with silk

Solution If a charged object placed near an uncharge object than redistribution of charge takes place in uncharge object and if we will earthed one surface of uncharged object than one charge goes to earth and other charge spread on its surface and it becomes charged.

12 >>For charges q₁ and q₂  separated by a distance R the magnitude of the electrostatic force is given by ?

• (A) F= q₁/(4 /pie E_o R²)
• (B) B . F= q₁ q₂/(4 /pie E_o R)
• (C) F= q₁ q₂/(4 /pie E_o R²)
• (D) F= q₁ q₂/(4 /pie E_o R³)

Solution c

13 >>The unit of charge is ?

• (A) ohm
• (B) ampere
• (C) couloumb
• (D) volt

Solution S.I. unit of charge is q=it =Ampere × sec = coulomb (C)

14 >>Electric field at a point is defined as ?

• (A) electric force experienced by two charges at that point
• (B) electric force per unit charge experienced by a unit charge at that point
• (C) electric force experienced by a dipole at that point
• (D) electric force experienced by a charge at that point

Solution Electric field intensity of a charge at a point is given by the force exerted by that charge on test charge or unit charge at that point

15 >>According to superposition of electric fields ?

• (A) The electric field of any combination of charges is the vector sum of the individual charges.
• (B) The electric field of any combination of charges is the scalar sum of the fields caused by the individual charges.
• (C) The electric field of any combination of charges is the vector sum of the fields caused by the individual charges.
• (D) The electric field of any combination of charges is the cross product of the individual fields.

Solution When several electric fields are working on single charge then the total electric field intensity on that charge is given by the vector sum of all electric field intensities

16 >>Electric field lines can be said to be ?

• (A) drawing lines of electric fields
• (B) drawing lines of electric fields
• (C) lines of equal Electric field
• (D) graphical representation of electric fields.

Solution When a tangent is drawn at any point on electric field line then that tangent gives the direction of electric field at that point so the electric field line represents the elec tric field.

17 >>At any point on S on an electric field line ?

• (A) the perpendicular to the line is in the direction of E⃗ at that point
• (B) the curvature is in the direction of E⃗  at that point
• (C) the binormal to the line is in the direction of E⃗ at that point
• (D) the tangent to the line is in the direction of E⃗  at that point

Solution When a tangent is drawn at any point on field line then that tangent gives the direction of electric field at that point

18 >>An electric dipole is ?

• (A) a pair of electric charges of equal magnitude q separated by a distance d
• (B) a pair of electric charges of equal magnitude q but negative sign, separated by a distance d
• (C) a pair of electric charges of equal magnitude q but opposite sign, separated by a distance
• (D) a pair of electric charges of equal magnitude q but positive sign, separated by a distance d

Solution Dipole is a combination of two equal and opposite charges separated by a very small distance.

19 >>The direction of an electric dipole ?

• (A) is from negative to positive charge
• (B) is perpendicular to line from negative to positive charge
• (C) is perpendicular to line from positive to negative charge
• (D) is from positive to negative charge

Solution Dipole Moment— It is a vector quantity and is directed from negative charge to positive charge along the axis. It is denoted as and is defined as the product of the magnitude of either of the charge and the dipole length i.e. p⃗ =q(2l⃗ )

20 >>Electric flux ?

• (A) Is a measure of the area of electric field through a surface
• (B) Is a measure of the electric field potential through a surface
• (C) Is a measure of the electric power through a surface
• (D) Is a measure of the flow (in analogy with flow of fluids) of electric field through a surface.

Solution Flux—It means flow Electric Flux—The number of electric field lines passing through any area normally known as electric flux. It is given by ϕ=E×area flux is a scalar quantity

21 >>Gauss's law states that ?

• (A) the total electric field flux coming out of a closed surface equals the net charge enclosed within the volume divided by ε₀
• (B) the total electric field flux coming out of a closed surface equals the charge enclosed within the volume divided by ε₀
• (C) the total electric field flux coming out of a closed surface equals the net charge enclosed within the volume
• (D) the total electric field flux coming out of an open surface equals the net charge enclosed within the volume divided by ε₀

Solution use Gauss Theorem

22 >>An electric dipole in an electric field experiences a torque τ ?

• (A) equal to the scalar product of p⃗   and E
• (B) equal to the vector product of E⃗  and p
• (C) equal to the scalar product of E⃗  and p
• (D) equal to the vector product of p⃗    and E

Solution ττ = pE Sinθ , the direction of torque or the direction of rotation of dipole is given by right hand palm rule or by Maxwell screw rule.

23 >>For a thin infinitely long straight wire of uniform linear charge density λ at a distance R from the wire The magnitude of E⃗  is ?

• (A) E=λ/3πϵ₀R
• (B) E==(λ/2πϵ₀R). Cosθ
• (C) E=λ²/2πϵ₀R
• (D) B . E=λ/4πϵ₀R

Solution use Electric field due to line charge or infinite wire

24 >>For an Infinite thin plane sheet of uniform surface charge density σ The magnitude of E⃗  is ?

• (A) E=σ/2ϵ₀
• (B) E=σ/2ϵ₀₃
• (C) E=σ²/2ϵ₀

(D) E=σ/ϵ₀

Solution use Electric field due to thin sheet

25 >>For a thin spherical shell of uniform surface charge density σ , The magnitude of E⃗  just outside is ?

• (A) E=4πR²σ/4πϵ₀r²
• (B) E=4πR²σ/4πϵ₀r³
• (C) E=4πRσ²/4πϵ₀r²
• (D) E=R²σ/4πϵ₀r²

Solution use Electric field due to hollow sphere or thin spherical shell

26 >>An electric field can deflect ?

• (A) γ - rays
• (B) X rays
• (C) Neutrons
• (D) α – rays

Solution Only alpha rays are moving with small velocity and having charge so they will be affected by electric field.

27 >>A conducting sphere of radius 5 cm is charged to 15 μ C. Another uncharged sphere of radius 10 cm is allowed to touch it for enough time. After the two are separated, the surface density of charge on the two spheres will be in the ratio ?

• (A) 0.0423611111111111
• (B) 0.125694444444444
• (C) 0.0430555555555556
• (D) 0.0840277777777778

Solution use coulomb's law

28 >>A Gaussian sphere encloses an electric dipole within it. Total flux across the sphere is ?

• (A) double that due to single charge
• (B) Zero
• (C) dependent on position of the charge
• (D) half that due to a single charge

Solution if a dipole is enclosed in a surface then flux is 0

29 >>A cylinder of radius R and length L is placed in an uniform electric field E parallel to the cylinder axis. The total flux for the surface of the cylinder is given by ?

• (A) πR²+πL²
• (B) 2πR²E
• (C) 0
• (D) πR²E

Solution Incoming flux =outgoing flux so net flux=0

30 >>A hollow spherical conductor of radius 2m carries a charge of 500 μ C. Then electric field strength at its surface is ?

• (A) Zero
• (B) 4.5×10⁶N/C
• (C) 1.125×10⁶N/C
• (D) 2.25×10⁶N/C

Solution c

31 >>When a negatively charged conductor is connected to earth, ?

• (A) Electrons flow from the earth to the conductor
• (B) Electrons flow from the conductor to the earth
• (C) Protons flow from the conductor to the earth
• (D) No charge flow occurs.

Solution After earthing a positively charged conductor electrons flow from earth to conductor and if a negatively charged conductor is earthed then electrons flows from conductor to earth.

32 >>Which of the following cannot be deflected by an electric field ?

• (A) γ - rays
• (B) X rays
• (C) α – rays
• (D) Both (a) and (b)

Solution Only alpha rays are moving with small velocity and having charge so they will be affected by electric field.

33 >>A tennis ball which has been covered with charges is suspended by a thread so that it hangs between two metal plates. One plate is earthed, while other is attracted to a high voltage generator. The ball ?

• (A) swings backward & forward hitting each plate in turn
• (B) is repelled by earthed plate and stays there.
• (C) hangs without moving
• (D) is attracted to the high voltage plate and stays there

Solution The plate which connected to high voltage generator induces negative charge on ball which causes attraction. When the ball strikes the positive plate, charge distribution again takes place that is the bass becomes positive and repulsion takes place. When it strikes the plate which connected to earth than its charge goes to earth and again it will be attracted towards positive plate. Hence the ball swings backward and forward hitting each plate in turn.

34 >>A metallic solid sphere is placed in a uniform electric field. In the figure, which path will the lines of force follow? ?

• (A) straight
• (B) curved
• (C) directed toward center
• (D) None of these

Solution The electric field is always perpendicular to the surface of a conductor. On the surface of a metallic solid sphere, the electrical field is oriented normally (i.e. directed towards the centre of the sphere)

35 >>Eight dipoles of charges of magnitude e are placed inside a cube. The total electric flux coming out of the cube will be ?

• (A) Zero
• (B) 16e/ϵ^o
• (C) A .8e/ϵ^o
• (D) e/ϵ^o

Solution On all the dipoles net charge=0 so theotal electric flux coming out of the surface

36 >>A charge q is placed at the center of the line joining two equal charges Q. The system of the three charges will be in equilibrium if q is equal to ?

• (A) Q/2
• (B) Q/3
• (C) Q/5
• (D) Q/4

Solution mod FA = mod FC

37 >>Four point charges qA=2μC,qB=−5μC,qC=2μC,andqD=−5μC are located at the corners of a square ABCD of side 10 cm. Force on a charge of 1μC placed at the centre of the square is ?

• (A) 3.6
• (B) 4.5
• (C) 1.8
• (D) 0

Solution the net electric field at centre=0 so force on charge 1µC=0

38 >>A system has two charges qA=2.5×10⁻⁷C and qB=−2.5×10⁻⁷C located at points A: (0, 0, –15 cm) and B: (0,0, +15 cm), respectively. What are the total charge and electric dipole moment of the system? ?

• (A) zero, 7.5×10⁻⁸Cm
• (B) zero, 8.5×10⁻⁸Cm
• (C) zero, 6.5×10⁻⁸Cm
• (D) zero, 5.5×10⁻⁸Cm

Solution a

39 >>An electric dipole with dipole moment 4×10⁻⁹C m is aligned at 30^∘ with the direction of a uniform electric field of magnitude 5×10⁴NC−1. Calculate the magnitude of the torque acting on the dipole. ?

• (A) 1.5×10⁻⁸Nm
• (B) 2.5×10⁻⁴Cm
• (C) 1.0×10⁻⁴Cm
• (D) 3.5×10⁻⁴Cm

Solution τ=pESinθ

40 >>Two insulated charged copper spheres A and B have their centres separated by a distance of 50 cm. What is the mutual force of electrostatic repulsion if the charge on each is 6.5×10⁻⁷C? The radii of A and B are negligible compared to the distance of separation. ?

• (A) 2.5×10⁻²N
• (B) 1.5×10⁻²N
• (C) 4.5×10⁻²N
• (D) 3.5×10⁻²N

Solution b

More Quiz >>> General Physics Quiz

Educational Website

Physics General Knowledge Questions