Topic 6: Fields and forces Flashcards
State Newton’s Universal Law of Gravitation
Any two bodies in the universe will attract each other with a force that is directly proportional to the product of their masses and inversely proportional to the square of the distance between them.
What are the conditions of Newton’s Universal Law of Gravitation? (4)
- the law only deals with point masses
- the masses in this equation are gravitational masses, which are equal and opposite even if the masses are not equal
- the forces are always attractive
- gravitation forces act between all objects in the Universe but only become significant if one or both of the objects involved are massive
Defining equation for Newton’s Universal Law of Gravitation
F ∝ (m1 m2) / r2
F = (G m1 m2) / r2
G is the universal gravitational constant = 6.67 X 10-11 N m2 kg-2
Define: gravitational field strength
The force per unit mass.
Defining equation for gravitational field strength
g = F / m
Where:
g is gravitational field strength in N kg-1
F is force in N
m is test mass in kg
What are the types of electric charge?
There are two types of electrical charge: positive and negative.
Why are charges known to exist?
Charges are known to exist because of the forces that exist between all charges, called the electrostatic force: like charges repel, unlike charges attract.
State and apply the law of conservation of charge
Equal amounts of positive and negative charge cancel each other. Matter that contains no charge, or matter that contains equal amounts of positive and negative charge, is said to be electrically neutral.
Describe and explain the difference in the electrical properties of conductors and insulators
A material that allows the flow of charge through it is called an electrical conductor. If charge cannot flow through a material it is called an electrical insulator. In solid conductors the flow of charge is always as a result of the flow of electrons from atom to atom.
State Coulomb’s Law
The electrical force between two charged objects is directly proportional to the product of the quantity of charge on the objects and inversely proportional to the square of the separation distance between the two objects.
Defining equation for Coulomb’s Law
F = (k q1 q2) / r2
Where:
F is the force in N
k is the Coulomb constant
q1 is the value of the first charge
q2 is the value of the second charge
r is the distance between the charges
Defining equation for electric field strength
E = F q2= force per positive unit test charge
What happens if a test charge is placed at any point in an electric field?
The value of the force that it feels at any point will depend on the value of the test charge only.
Relate the electric field around a point charge to the charge producing the field.
E = q1 / 4 π ε0 r2
Where:
E is the electric fiels around a point charge
q1 is the charge producing the field
ε0 is permittivity of free space = 8.85 X 10-12 C2 N-1 m-2
r is the distance between the charges
What is the electric field pattern for a positive point charge?
What is the electric field pattern for a negative point charge?
What is the electric field pattern for a positively charged sphere?
What is the electric field pattern for a negatively charged sphere?
What is the electric field pattern for two like point charges?
What is the electric field pattern for two different point charges?
What is the electric field pattern for oppositely charged parallel plates?
Magnetic field pattern due to a current in a straight wire
Magnetic field pattern due to a flat, cicular coil (cross-section)
