Electric Fields Flashcards
What are electrical conductors?
Material that contains lots of free electrons, that aren’t attached to a particular atom, so can conduct electricity.
What are electrical insulators?
Materials that don’t contain free electrons so each is attached to an individual atom so it can’t conduct electricity.
How does a gold leaf electroscope work?
If a charged particle is in contact with the metal cap, some of the charge on the object transfers to the electroscope. The gold leaf and metal stem gain the same type of charge and the leaf rises as it is repelled by the stem. If another object of the same type of charge is brought near the electroscope, the leaf rises further as the object forces some charge on the cap to transfer to the leaf and stem.
What is a field line?
The direction of the field line indicates the direction and path followed by a free positive test charge. Smaller space between field lines means greater magnitude of charge.
Field diagram for two oppositely charged point charges
Field lines from positive charge to negative charge. Never cross each other. Join point masses perpendicularly. All are curves apart from shortest route.
Filed diagram for point charge with oppositely charged flat plate
Filed lines from positive to negative. Lines join perpendicular to point charge and plate. Lines never cross. Join all across plate.
Field diagram for two oppositely charged flat, parallel plates
Field lines from positive to negative. Lines run parallel from one plate to the other, meeting at right angles (except near edges of field). The field is uniform between the two plates because the field line are parallel.
What is the electric field strength (E) at a point in an electric field?
The force per unit charge on a small positively charged object at that point in the field. Unit newtons per coulomb.
What is a uniform field?
A region where the field strength is the same in magnitude and direction at every point in the field. Eg electric field between two oppositely charged parallel plates.
What does electric field strength depend on?
Charge on the body. Greater charge means stronger field. Concentration of charge. Larger surface area for same charge means weaker field.
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What happens in terms of energy when a charged particle is moved closer to another particle of the same type of charge?
Work is done to move the particle closer. The electric potential energy of each increases.
What is electric potential at a point in an electric field?
The work done per unit positive charge on a small positively charged object (positive test charge) to move it from infinity to that point in the field. Unit volt.
Is also the electric potential energy over charge of particle.
Equipotentials
Lines in an electric field along which the electric potential is constant. A test charge moving along it has constant potential energy and no work is done on it by the electric field because the force due to the field is at right angles to the equipotential.
Potential gradient at a point in an electric field
The change of potential per unit change of distance along the field line at that point. It is the negative of the electric field strength.
Coulomb’s law
The force between two point charges in a vacuum is proportional to the magnitude of the product of the charges and inversely proportional to the square of the distance between them. Air may be treated as a vacuum.
