Home
Class 12
PHYSICS
An oil drop carrying a charge q has a ma...

An oil drop carrying a charge q has a mass m kg. If is falling freely in air with terminal speed v. The electric field required to make the drop move upwards with the same speed is

A

`(mg)/q`

B

`(2mg)/q`

C

`(mgv)/q^(2)`

D

`(2mgv)/q`

Text Solution

Verified by Experts

The correct Answer is:
B
Promotional Banner

Similar Questions

Explore conceptually related problems

A 0.1 m long conductor carrying a current of 50 A is held perpendicular to a magnetic field of 1.25 mT. The mechanical power required to move the conductor with a speed of 1ms^(-1) is

A long , straight wire carries a current i. A particle having a positive charge q and mass m, kept at a distance x_0 from the wire is projected towards it with a speed v. Find the minimum separation between the wire and the particle.

Figure shows a metal rod PQ resting on the smooth rails AB and positioned between the poles of a permanent magnet. The rails, the rod and the magnetic field are in three mutually perpendicular directions. A galvonometer G connects the rails through a switch K. Length of rod = 15 cm, B = 0.50 T, resistance of the closed loop containing the rod = 9.0mOmega . Assume the field to be uniform. a. Suppose K is open and the rod is moved with a speed of 12cms^(-1) in the direction shown. Give the polarity and magnitude of the induced emf. b. Is there an excess charge built up at the ends of the rods when K is open? What if K is closed? c. With K open and the rod moving uniformly, there is no net force on the electrons in the rod PQ eventhough they do experience magnetic force due to the motion of the rod. Explain. d. What is the retarding force on the rod when K is closed? e. How much power is required (by an external agent) to keep the rod moving at the same speed (=12cms^(-1)) when K is closed? How much power is required when K is open? f. How much power is dissipated as heat in the closed circuit? What is the source of this power? g. What is the induced emf in the moving rod if the magnetic field is parallel to the rails instead of being perpendicular?

Two particles, carrying charges -q and +q and having equal masses m each, are fixed at the rod is clamped at an end and is placed in a uniform electric field E with the axis of the dipole along the electric field. The rod is slightly tlted and then released. Neglecting gravity find the time period of small oscillations.

A particle having mass m and charge q is released from the origin in a region in which electric field and magnetic field are given by vecB =- B_0vecJ and vecE - E_0 vecK. Find the speed of the particle as a function of its z-coordinate.

In a Millikan-type oil-drop experiment, the plates are 8 mm apart. An oil drop is found to remain at rest when the upper plate is at a potential 136 V higher than that of the lower one. When the electric field is switched off, the drop is found to fall a distance of 2.0 mm in 36 seconds with a uniform speed. Find (a) the charge on the drop and (b) the number of electrons attached to this drop. Density of oil = 880 kg m^(-3) and coefficient of viscosity of air = 180 mupoise .

An electric current I enters and leaves a uniform circular wire of radius a through diametrically opposite points. A charged paricle q moving along the axis of the circular wire passes through its centre at speed v. The magnetic force acting on the particle when it passes through the centre has a magnitude

A tightly-wound, long solenoid has n turns per unit length, a radius r and carries a current i. A particle having charge q and mass m is projected from a point on the axis in a direction perpendicular to the axis. What can be the maximum speed for which the particle does not strike the solenoid?

A non - conducting sphere has mass of 100 g and radius 20 cm . A flat compact coil of wire with turns 5 is wrapped tightly around it with each turns concentric with the sphere. This sphere is placed on an inclined plane such that plane of coil is parallel to the inclined plane. A uniform magnetic field of 0.5 T exists in the region in vertically upwards direction. Compute the current I required to rest the sphere in equilibrium. (##SUR_PHY_XII_V01_C03_E04_005_Q01##)

A wire ab of length l, mass m and resistance R slides on a smooth, thick pair of metallic rails joined at the bottom as shown in the figure . The plane of the the rails makes an angle theta with the horizontal. A vertical magnetic field B exists in the region. if the wire slides on the rails at a constant speed v, show that B = sqrt (mg R sin theta)/ sqrt (vl^2 cos^2theta) .