Electric Field Flashcards
What is Coulomb’s law of electrostatic?
It states that electric force is directly proportional to the product of two point charges and inversely proportional to the square of their separation
What is electric field?
Electric field is a region of space where a charge experiences an electric force
What is the direction of electric field?
The direction of force on a positive charge
What does electric field lines show?
The direction of force acting on a stationary positive point charge in the field
What are the properties of electric field lines?
- electric field lines do not cross or touch
- electric field lines are perpendicular to any conducting surface
- number of field lines entering or leaving a charge is proportional to the magnitude of charge
What does a higher density of electric field lines mean?
Stronger electric field
Can electric field lines pass through a conductor?
No
Can electric field lines pass through an insulator?
Yes
What do the field lines of uniform electric field look like?
Parallel and equally spaced
For non-linear electric field lines, what is the direction of electric field?
Direction of electric field E is tangent to the electric field lines at each point
What is electric field strength?
Electric force per unit charge that acts on a small stationary positive test charge placed at that point. Its magnitude equals to the potential gradient at that point
Why must test charge be small?
To prevent distortion of electric field that is present due to another charge
Why must test charge be stationary?
A test charge that moves in a non-uniform electric field or non-parallel magnetic field would experience varying forces at different positions
What is electric potential?
Electric potential is the work done per unit positive charge in bringing a small test charge from infinity to that point by an external agent at constant kinetic energy
What is the relationship between electric field strength E and potential V?
- E is always pointing towards decreasing V
- E and V are always perpendicular to each other
- E is numerically equal to the potential gradient -dV/dr
What is the physical meaning of the negative sign in equation E = -dV/dR?
electric field strength is always pointing towards decreasing potential
Why is gravitational potential always negative whereas values of electric potential can be positive or negative?
- Gravitational force is always attractive and thus work done by external agent is always negative when mass is brought from infinity
- Electrical force can be either attractive or repulsive and thus when charge is brought from infinity, work done by external agent is positive for charges of same sign and negative for charges of opposite sign
Why electric field lines always intersect a charged plate at 90° to the surface of the plate?
- Electric potential is constant, so electric field strength is zero on its surface
- no force will be acting on the charge, hence no work is done when a positive test charge is moved along the surface
- electric field lines which represent the direction of electric field strength and force must be perpendicular to the surface of the plate
What is electric potential energy?
Work done in moving a point charge from infinity to that point by an external agent at constant speed
Two parallel plates are separated by a distance d with a potential difference of V, how to show that the magitude of electric field strength E is numerically equal to potential gradient?
- Electric force F acting on a charge q is qE
- work done W = external force F × displacement d = qEd
- By applying definition for electric potential, W = qV
- qV = qEd, E = V/d
What is an electronvolt?
A unit of energy that equals to the energy gained by an electron when it is accelerated through a potential difference of 1 volt
