Near the surface of earth, an electric field points radially downward and has a magnitude of approximately 100N/C.
What charge (magnitude and sign) would have to be placed on a penny that has a mass of 3.11g to cause it to rise into the air with an upward acceleration of 1.990 `m/s ^2` ? (Express your answer to three significant figures)

Figure shows some of the electric field lines due to three point charges q_, q_2 and q_3 of equal magnitude. What are the signs of each of the three charges?

Fig. shows some of the electric field lines due to three point charges arranged along the vertical axis. All three charges have the same magnitude. (a) What are the signs of each of the three charges? Explain your reasoning. (b) At what points(s) is the magnitude of the electric field the smallest? Explain your reasoning. Explain how the fields produced by each individual point charge combine to give a small net field at this point or points. (c ) Two point charges q and -q are placed at a distance d apart. What are the points at which the resultant electric field is parallel to the line joining the two charge? .

A spherical conductor of radius 10 cm has a charge of 3.2 x 10^-7 C distributed uniformly. What is magnitude of electric field at point 15 cm from centre of sphere?

A charge particle is moving with a velocity 3hat(i) + 4 hat(j) m//sec and it has electric field E = 10hat(k) N//C at a given point. Find the magnitude of magneitc field at the same point due to the motion of the charge particle.

Answer the following: (a) Derive and expression for the electric field at any point on the equatorial line of an electric dipole. (b) Two identical point charges, q each kept 2m apart in air. A third point charge Q of unknown magnitude and sign is placed on the line joining the charges such that the system remains in equilibrium. Find the position and nature of Q.

Two blocks of masses 2.9 kg and 1.9 kg are suspended from a rigid support S by two inextensible wires each of length 1 m. The upper wire has negligible mass and the lower wire has a uniform mass of 0.2 kg/m. Thewhole system of block, wire and support have an upward acceleration of 0.2 m/s2. g = 9.8 m/s2. The tension at the mid-point of lower wire is-

Two block of mass 2.9 kg and 1.9 kg are suspended from a rigid support S by two inextensible wires each of length 1 m , as shown in figure. The upper wire has negligible mass and the lower wires and support have an uniformly mass of 0.2 kg .The whole system of blocks, wire and support have an upwards acceleration of 0.2 m//s^(2) . Acceleration due to gravity is 9.8 m//s^(2) . (a) Find the tension at the mid point of the lower wire. (b)Find the tension at the mid point of the upper wire.

The cube shown in Fig. 2.119 has sides of length L = 10.0 cm . The electric field is uniform , has a magnitude E = 4.00 xx 10^(3) NC^(-1) and is parallel to the xy plane at an angle of 37^(@) measured from the + x - axis toward the + y - axis . The surface that have zero flux are

A charged cloud system produces an electric field in the air near the earth's surface. A particle of charge -2xx10^(-9) C is acted on by a downward electrostatic force of 3xx10^(-6) N when placed in this field. The gravitational and electrostatic force, respectively, exerted on a proton placed in this field are

A uniform ring of mass m is placed on a rough horizontal fixed surface as shown in the figure. The coefficient of friction between the left part of the ring and left part of the horizontal surface is mu_(1)=0.6pi and between right half and the surface is mu_(2)=0.2pi . At the instant shown, now the ring has been imparted an angular velocity in clockwise sense in the figure shown. At this moment magnitude of acceleration of centre O of the ring (in m//s^(2) ) is (take g=10m//s^(2) )