Tiêu đề 1.ELECTRIC CHARGES AND FIELDS - Questions.pdf ✅

1.ELECTRIC CHARGES AND FIELDS (1.)The capacity and the energy stored in a parallel plate condenser with air between its plates are respectively C0 and W0. If the air is replaced by glass (dielectric constant = 5) between the plates, the capacity of the plates and the energy stored in it will respectively be (a.) 5C0, 5W0 (b.) 5C0, W0 5 (c.) C0 5 , 5W0 (d.) C0 5 , W0 5 (2.)An electron initially at rest falls a distance of 1.5 cm in a uniform electric field of magnitude 2× 104 N/C. The time taken by electron to fall this distance is (a.) 1.3 × 102 s (b.) 2.1 × 10−12 s (c.) 1.6 × 10−10 s (d.) 2.9 × 10−9 s (3.)Two charges each equal to ηq(η −1 < √3) are placed at corners of an equilateral triangle of side a. The electric field at the third corner is E3 then (where E0 = q/4πε0a 2 ) (a.) E3 = E0 (b.) E3 < E0 (c.) E3 > E0 (d.) E3 ≥ E0 (4.)When a slab of dielectric material is introduced between the parallel plates of a capacitor which remains connected to a battery, then charge on plates relative to earlier charge (a.) Is less (b.) Is same (c.) Is more (d.) May be less or more depending on the nature of the material introduced (5.)An air filled parallel plate capacitor the capacity C. If distance between plates is doubled and it is immersed in a liquid then capacity becomes twice. Dielectric constant of the liquid is (a.) 1 (b.) 2 (c.) 3 (d.) 4 (6.)Top of the stratosphere has an electric field E (in units of V/m) nearly equal to (a.) 0 (b.) 10 (c.) 100 (d.) 1000 (7.)Two capacitor of capacitance 2μF and 3μF are joined in series. Outer plate first capacitor is at 1000 volt and outer plate of second capacitor is earthed (grounded). Now the potential on inner plate of each capacitor will be (a.) 700 Volt (b.) 200 Volt (c.) 600 Volt (d.) 400 Volt (8.)An air capacitor of capacity C = 10μF is connected to a constant voltage battery of 12 V. Now the space between the plates is filled with a liquid of dielectric constant 5. The charge that flows now from battery to the capacitor is (a.) 120μC (b.) 699μC (c.) 480μC (d.) 24μC (9.)A point charge of 1.8μC is at the centre of cubical Gaussian surface 55cm on edge. What is the net electric flux through the surface? (a.) 1.0 × 105N − m2C −1 (b.) 3.0 × 105N − m2C −1 (c.) 2.0 × 105N − m2C −1 (d.) 4.0 × 105N − m2C −1 (10.)Two identical metal spheres charged with + 12μF and -8μF are kept at certain distance in air. They are brought into contact and then kept at the same distance. The ratio of the magnitudes of electrostatic forces between them before them and after contact is (a.) 12:1 (b.) 8:1 (c.) 24:1 (d.) 4:1 (11.)The potential of the electric field produced by point charge at any point (x, y, z) is given by V = 3x 2 + 5, where x, y are in metres and V is in volts. The intensity of the electric field at (-2,1,0) is (a.) +17 Vm−1 (b.) −17 Vm−1 (c.) +12 Vm−1 (d.) −12 Vm−1 (12.)Two large metal plates are placed parallel to each other. The inner surfaces of plates are charged by +σ and – σ(cm−2). The outer surfaces are neutral. The electric field in the region between the plates and outside the plates is (a.) 2σ ε0 , σ ε0
(b.) σ ε0 , zero (c.) 2σ ε0 , zero (d.) zero, 2σ ε0 (13.)Three identical capacitors are given a charge Q each and they are then allowed to discharge through resistance R1, R2 and R3. Their charges, as a function of time shown in the graph below. The smallest of the three resistance is (a.) R3 (b.) R2 (c.) R1 (d.) Cannot be predicted (14.)In nature, the electric charge of any system is always equal to (a.) Half integral multiple of the least amount of charge (b.) Zero (c.) Square of the least amount of charge (d.) Integral multiple of the least amount of charge (15.)Three equal charges are placed on the three corners of a square. If the force between q1 and q2 is F12 and that between q1 and q3 is F13, the ratio of magnitudes F12 F13 is (a.) 1/2 (b.) 2 (c.) 1/√2 (d.) √2 (16.)The respective radii of the two spheres of a spherical condenser are 12 cm and 9 cm. The dielectric constant of the medium between them is 6. The capacity of the condenser will be (a.) 240 pF (b.) 240 μF (c.) 240 F (d.) None of the above (17.)All capacitors used in the diagram are identical and each is of capacitance C. Then the effective capacitance between the points A and B is (a.) 1.5C (b.) 6C (c.) C (d.) 3C (18.)Two protons A and B are placed in space between plates of a parallel plate capacitor charged upto V volts (see fig.) Force on protons are FA and FB then (a.) FA > FB (b.) FA < FB (c.) FA = FB (d.) Nothing can be said (19.)The force of interaction between two charges q1 = 6μ C and q2 = 2μC is 12 N. If charge q = −2μC is added to each of the charges, then the new force of interaction is (a.) 2 × 10−7 N (b.) Zero (c.) 30 N (d.) 2 × 10−3 N (20.)Three capacitor each of 6μF are available. The minimum and maximum capacitances which may be obtained are (a.) 6μF, 18μF (b.) 3μF, 12μF (c.) 2μF, 12μF (d.) 2μF, 18μF (21.)Electric field intensity at a point in between two parallel sheets with like charges of same surface charge densities (σ) is (a.) σ 2ε0 (b.) σ ε0 (c.) Zero (d.) 2σ ε0 (22.)Energy associated with a moving charge is due to a (a.) Electric field (b.) Magnetic field (c.) Both electric field and magnetic field (d.) None of these (23.)A conducting sphere of radius R = 20 cm is given a charge Q = 16μC. What is E⃗ at centre (a.) 3.6 × 106 N/C (b.) 1.8 × 106 N/C (c.) Zero (d.) 0.9 × 106 N/C (24.)If Ea be the electric field strength of a short dipole at a point on its axial line and Ee that on equatorial line at the same distance, then
(a.) Ee = 2Ea (b.) Ea = 2Ee (c.) Ea = Ee (d.) None of these (25.)Four charges equal to −Q are placed at the four corners of a square and a charge q is at its centre. If the system is in equilibrium the value of q is (a.) − Q 4 (1 + 2√2) (b.) Q 4 (1 + 2√2) (c.) − Q 2 (1 + 2√2) (d.) Q 2 (1 + 2√2) (26.)4 point charges each +q is placed on the circumference of a circle of diameter 2d in such a way that they form a square. The potential at the centre is (a.) 0 (b.) 4q d (c.) 4d q (d.) q 4d (27.) The electric intensity outside a charged sphere of radius R at a distance r(r > R) is (a.) σR 2 ε0r 2 (b.) σr 2 ε0R2 (c.) σr ε0R (d.) σR ε0r (28.)The ratio of electrostatic and gravitational forces acting between electron and proton separated by a distance 5 × 10−11m, will be (Charge on electron = 1.6 × 10−19C, mass of electron = 9.1 × 10−31kg, mass of proton = 1.6 × 10−27kg, G = 6.7 × 10−11Nm2 /kg 2 ) (a.) 2.36 × 1039 (b.) 2.36 × 1040 (c.) 2.34 × 1041 (d.) 2.34 × 1042 (29.)A parallel plate condenser with a dielectric of dielectric constant K between the plates has a capacity C and is charged to a potential V volts. The dielectric stab is slowly removed from between the plates and then reinserted. The net work done by the system in this process is (a.) 1 2 (K − 1)CV 2 (b.) CV 2 (K − 1)/K (c.) (K − 1)CV 2 (d.) Zero (30.)A cube of side l is placed in a uniform field E, where E = Eî. The net electric flux through the cube is (a.) Zero (b.) l 2E (c.) 4l 2E (d.) 6l 2E (31.)The displacement of a charge Q in the electric field E⃗ = e1î+ e2ĵ+ e3k̂ is r = aî+ bĵ. The work done is (a.) Q(ae1 + be2) (b.) Q√(ae1 ) 2 + (be2 ) 2 (c.) Q(e1 + e2)√a 2 + b 2 (d.) Q (√e1 2 + e2 2) (a + b) (32.)In the following figure two parallel metallic plates are maintained at different potential. If an electron is released midway between the plates, it will move (a.) Right ward at constant speed (b.) Left ward at constant speed (c.) Accelerated right ward (d.) Accelerated left ward (33.)Electric potential is given by V = 6x − 8xy 2 − 8y + 6yz − 4z 2 Then electric force acting on 2C point charge placed on origin will be (a.) 2N (b.) 6N (c.) 8N (d.) 20N (34.)In Millikan’s oil drop experiment an oil drop carrying a charge Q is held stationary by a potential difference 2400 V between the plates. To keep a drop of half the radius stationary the potential difference had to be made 600 V. What is the charge on the second drop (a.) Q 4 (b.) Q 2 (c.) Q (d.) 3Q 2 (35.)The unit of electric field is not equivalent to (a.) N/C (b.) J/C (c.) V/m (d.) J/C − m (36.)Two dielectric slabs of constant K1 and K2 have been filled in between the plates of a capacitor as shown below. What will be the capacitance of the capacitor
(a.) 2ε0A d (K1 + K2) (b.) 2ε0A d ( K1+K2 K1×K2 ) (c.) 2ε0A 2 ( K1×K2 K1+K2 ) (d.) 2ε0A d ( K1×K2 K1+K2 ) (37.)The electric intensity due to a dipole of length 10 cm and having a charge of 500μC, at a point on the axis at a distance 20 cm from one of the charges in air, is (a.) 6.25 × 107 N/C (b.) 9.28 × 107 N/C (c.) 13.1 × 1111 N/C (d.) 20.5 × 107 N/C (38.)Two unlike charges of magnitude q are separated by a distance 2d. The potential at a point midway between them is (a.) Zero (b.) 1 4πε0 (c.) 1 4πε0 . q d (d.) 1 4πε0 . 2q d2 (39.)For the circuit shown, which of the following statements is true (a.) With S1 closed, V1 = 15 V, V2 = 20 V (b.) With S3 closed V1 = V2 = 25V (c.) With S1 and S2 closed V1 = V2 = 0 (d.) With S1 and S3 closed, V1 = 30V, V2 = 20V (40.)The charge on any one of the 2μ F capacitors and 1μ F capacitor will be given respectively (in μ C) as (a.) 1,2 (b.) 2,1 (c.) 1,1 (d.) 2,2 (41.)Charges +2q, +q and +q are placed at the corners A, B and C of an equilateral triangle ABC. If E is the electric field at the circumcentre O of the triangle, due to the charge +q, then the magnitude and direction of the resultant electric field at O is (a.) E along AO (b.) 2E along AO (c.) E along BO (d.) E along CO (42.)n identical condensers are joined in parallel and are charged to potential V. Now they are separated and joined in series. Then the total energy and potential difference of the combination will be (a.) Energy and potential difference remain same (b.) Energy remains same and potential difference is nV (c.) Energy increases n times and potential difference is nV (d.) Energy increases n times and potential difference remains same (43.)The charge on a capacitor of capacitance 10μF connected as shown in the figure is (a.) 20μC (b.) 15μC (c.) 10μC (d.) Zero (44.)The total electric flux through a cube when a charge 8q is placed at one corner of the cube is (a.) ε0q (b.) ε0 q (c.) 4πε0q (d.) q ε0 (45.)The electric field between the two spheres of a charged spherical condenser (a.) Is zero (b.) Is constant (c.) Increases with distance from the Centre (d.) Decreases with distance from the Centre (46.)Two capacitors of 3pF and 6pF are connected in series and a potential difference of 5000 V is applied across the combination. They are then disconnected and reconnected in parallel. The potential between the plates is (a.) 2250V (b.) 2222V (c.) 2.25 × 106V (d.) 1.1 × 106V 2F 2F 1F 2V