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Grade 11Electric Current

Both the capacitor are made of square plates of edge a . The separation between the plates of capacitor are d1 d2 . A potential difference V is applied between the points a and b . An electron is projected between the plates of the upper capacitor along the central along the central line . With what minimum speed should the electron be projected so that it does not Collide with any plate? . Consider only electric forceExplain withstep???????

Profile image of Radhika Batra
12 Years agoGrade 11
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Profile image of Askiitians Tutor Team
ApprovedApproved Tutor Answer1 Year ago

To determine the minimum speed at which an electron must be projected between the plates of a capacitor without colliding with either plate, we need to analyze the forces acting on the electron and the geometry of the setup. Let's break this down step by step.

Understanding the Setup

We have two parallel plates forming a capacitor, each with a square shape and edge length a. The distance between the plates is d, which can be either d1 or d2. When a potential difference V is applied across the plates, an electric field E is created between them.

Electric Field Calculation

The electric field E between two parallel plates is given by the formula:

  • E = V/d

Here, V is the potential difference and d is the separation between the plates. This electric field exerts a force on the electron.

Force on the Electron

The force F acting on the electron due to the electric field is calculated using:

  • F = qE

Where q is the charge of the electron (approximately -1.6 x 10-19 C). Since the electron is negatively charged, the direction of the force will be opposite to the direction of the electric field.

Motion of the Electron

When the electron is projected with an initial speed v along the central line between the plates, it will experience a downward acceleration due to the electric field. This acceleration a can be calculated using Newton's second law:

  • a = F/m

Where m is the mass of the electron (approximately 9.11 x 10-31 kg). Substituting the force, we get:

  • a = (qE)/m = (qV)/(md)

Time of Flight

Next, we need to determine how long the electron will be in the region between the plates. The time t it takes for the electron to travel the distance d horizontally (assuming it travels the entire length of the plates) can be expressed as:

  • t = d/v

Vertical Displacement

During this time, the electron will also experience vertical displacement due to the electric field. The vertical displacement y can be calculated using the kinematic equation:

  • y = (1/2)at2

Substituting for a and t, we have:

  • y = (1/2) * (qV/(md)) * (d/v)2

Condition for No Collision

To ensure that the electron does not collide with the plates, the vertical displacement y must be less than half the distance between the plates:

  • y < d/2

Substituting our expression for y gives:

  • (1/2) * (qV/(md)) * (d/v)2 < d/2

By simplifying this inequality, we can solve for the minimum speed v:

  • v > sqrt((qVd)/(m))

Final Expression

Thus, the minimum speed at which the electron must be projected to avoid colliding with the plates is:

  • v_{min} = sqrt((qVd)/(m))

In summary, by considering the forces acting on the electron and the geometry of the capacitor, we can derive the minimum speed required to prevent collisions with the plates. This approach combines principles of electric fields, forces, and kinematics to arrive at a clear solution.