Tiêu đề 01. ELECTRIC CHARGES AND FIELDS.pdf ✅

#QID# 38028 (1.) Two point charges A and B , having charges +Q and −Q respectively, are placed at certain distance apart and force acting between them is F. If 25% charge of A is transferred to B , then force between the charges becomes : [2019] (1) F (2) 9 F 16 (3) 16 F 9 (4) 4 F 3 #QID# 38029 (2.) Two metal spheres, one of radius R and the other of radius 2R respectively have the same surface charge density  . They are brought in contact and separated. What will be the new surface charge densities on them? [NEET Odisha 2019] (1) 1 2 5 5 , 3 6     = = (2) 1 2 5 5 , 6 2     = = (3) 1 2 5 5 , 2 6     = = (4) 1 2 5 5 , 2 3     = = #QID# 38030 (3.) Suppose the charge of a proton and an electron differ slightly. One of them is - e, the other is (e+Δe) . If the net of electrostatic force and gravitational force between two hydrogen atoms placed at a distance d (much greater than atomic size) apart is zero, then Δe is of the order of [Given mass of hydrogen 27 m 1.67 10 kg h − =  ][2017] (1) 23 10 C − (2) 37 10 C − (3) 47 10 C − (4) 20 10 C − #QID# 38031 (4.) Two identical charged spheres suspended from a common point by two massless strings of lengths l , are initially at a distance d(d )  l apart because of their mutual repulsion. The charges begin to leak from both the spheres at a constant rate. As a result, the spheres approach each other with a velocity v . Then v varies as a function of the distance x between the spheres, as :[2016] (1) 1 2 v x  (2) v x  (3) 1 2 v x  (4) 1 v x− 
#QID# 38032 (5.) Two pith balls carrying equal charges are suspended from a common point by strings of equal length. The equilibrium separation between them is r . Now the strings are rigidly clamped at half the height. The equilibrium separation between the balls now become[2013] (1) 3 2   r     (2) 2 3   r     (3) 2 3   r     (4) 2 2   r     #QID# 38033 (6.) A charge ' q ' is placed at the centre of the line joining two equal charges ' Q '. The system of the three charges will be in equilibrium if ' q ' is equal to[NEET Kar. 2013, 1995] (1) Q /2 (2) −Q /4 (3) Q /4 (4) −Q /2 #QID# 38034 (7.) Two metallic spheres of radii 1 cm and 3 cm are given charges of 2 1 10 C− −  and 2 5 10 C−  , respectively. If these are connected by a conducting wire, the final charge on the bigger sphere is :[2012M] (1) 2 2 10 C−  (2) 2 3 10 C−  (3) 2 4 10 C−  (4) 2 1 10 C−  #QID# 38035 (8.) Two positive ions, each carrying a charge q , are separated by a distance d . If F is the force of repulsion between the ions, the number of electrons missing from each ion will be ( e being the charge of an electron)[2010]
(1) 2 0 2 4 Fd e  (2) 2 0 2 4 Fe d  (3) 2 0 2 4 Fd e  (4) 2 0 2 4 Fd q  #QID# 38036 (9.) An electron is moving round the nucleus of a hydrogen atom in a circular orbit of radius r . The Coulomb force F between the two is [2003] (1) 2 3 e K r r (2) 2 ˆ 2 e K r r (3) 2 ˆ 3 e K r r − (4) 2 3 e K r r − ( where 0 1 4 K   =   #QID# 38037 (10.) When air is replaced by a dielectric medium of force constant K , the maximum force of attraction between two charges, separated by a distance[1999] (1) decreases K-times (2) increases K-times (3) remains unchanged (4) becomes 2 1 K times #QID# 38038 (11.) Point charges + − 4 , q q and +4q are kept on the X -axis at points x x a = = 0, and x a = 2 respectively. Then[1988] (1) only −q is in stable equilibrium (2) none of the charges is in equilibrium (3) all the charges are in unstable equilibrium (4) all the charges are in stable equilibrium. #QID# 38039
(12.) A spherical conductor of radius 10 cm has a charge of 7 3.2 10 C−  distributed uniformly. What is the magnitude of electric field at a point 15 cm from the centre of the sphere? [2020] D) 9 2 2 0 1 9 10 Nm / C 4     =    (1) 5 1.28 10 N / C  (2) 6 1.28 10 N / C  (3) 7 1.28 10 N / C  (4) 4 1.28 10 N / C  #QID# 38040 (13.) Two parallel infinite line charges with linear charge densities +C / m and −C / m are placed at a distance of 2R in free space. What is the electric field mid-way between the two line charges?[2019] (1) zero (2) 0 2 N / C R    (3) 0 N / C R    (4) 0 N / C 2 R   #QID# 38041 (14.) A hollow metal sphere of radius R is uniformly charged. The electric field due to the sphere at a distance r from the centre :[2019] (1) increases as r increases for r R  and for r R  (2) zero as r increases for r R  , decreases as r increases for r R  (3) zero as r increases for r R  , increases as r increases for r R  (4) decreases as r increases for r R  and for r R  #QID# 38042 (15.) An electron falls from rest through a vertical distance h in a uniform and vertically upward directed electric field E. The direction of electric field is now reversed, keeping its magnitude the same. A proton is allowed to fall from rest in it through the same vertical distance h . The time of fall of the electron, in comparison to the time of fall of the proton is[2018] (1) smaller (2) 5 times greater (3) equal (4) 10 timesgreater #QID# 38043 (16.) A toy car with charge q moves on a frictionless horizontal plane surface under the influence of a uniform electric field E . Due to the force q E , its velocity increases from 0 to 6 m / s in one second duration. At that instant the direction of the field is reversed. The car continues to move for two more seconds under the influence of this