Electric and Magnetic Fields Flashcards
What is an electric field
A region in which a charged particle experiences a non-contact force, attraction or repulsion. Like a force field.
What is electric charge measured in
Coulombs
What happens when a charged object is placed in an electric field
The object will experience a force
If the charged object is a uniformly charged sphere, what do you assume
Assume all of its charge is at its centre, it behaves like a point charge with a radial field.
How are electric fields represented
With field lines
What does coulombs law tell you
The force of attraction or repulsion between 2 point charges in a vacuum.
What is coulombs law
F = Q1Q2/4piE_0r^2
What is the relationship between Q1 and Q2 in coulombs law
The FORCE on Q1is always equal and opposite to the force on Q2, the direction of the force depends on the charges. This means regardless of their attraction, the force on Q1 and Q2 will always be equal and opposite
What happens to force between charged particles as they get further apart
Coulombs law is an inverse square law, the further apart the charges, the weaker the force between them.
What happens to Coulombs law if the particles are not in a vacuum
E_0, permittivity in vacuum, is replaces by E, permittivity of the material they are in. Air is treated as a vacuum.
How do you treat the permittivity of air when using coulombs law
Permittivity of air is same as permittivity in vacuum. Keep it as E_0
How do you experimentally measure the force between 2 charges
Use an electronic balance. Fix a charged sphere to a mass balance and zero the balance. Clamp another charged sphere carrying the same charge directly above the first sphere (make sure the 2 don’t touch). The spheres will repel each other, causing the lower sphere to push down on the scale, so the scales will register a mass. Convert mass reading on the scales into a force using F=W=mg
If you vary the distance between spheres, r, then you should find F is directly proportional to 1/r^2
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How do you charge spheres in the experiment to find force between 2 charges
By connecting the spheres to a power supply
What is electric field strength, E
Force per unit positive charge. The force that a charge of +1C would experience if placed in the electric field.
What is the equation for electric field strength
E = F/Q
What are the units for electric field strength
N C^-1
How does electric field strength vary in a radial field and in a uniform field
In a radial field, electric field strength depends on where you are in the field. In uniform field, electric field strength is the same everywhere
What direction is electric field strength pointing in
Electric field strength is a vector pointing in the direction that a positive charge would move
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What type of field does a point charge have
Radial field
Where is electric field the strongest in a radial field
The area where the field lines are closest together, highest field line density area
Which direction would the field lines on a radial field point for a negatively charged particle
Point towards the particle. Field lines point in the direction a proton would travel, and protons are attracted to negative charge, so they would go towards negative charge.
Which direction would the field lines on a radial field point for a positively charged particle
Away from the particle
What does the electric field strength depend on in a radial field
The distance from the point charge and magnitude of charge on point charge
How does electric field strength decrease as you get further away from the point charge in a radial field
Inverse squarely. E is inversely proportional to r^2. The further away the field lines are from each other, the weaker the electric field strength on a radial field.
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