Electric Fields - Coulomb's Law, strength and types Flashcards
What is a field?
A field is a region of space where an object experiences a force.
What is an electric field?
An electric field is a region of space where a charged object experiences a force.
What are the three types of fields?
- Electric
- Gravitational
- Magnetic
What does the ‘r’ stand for in Coulomb’s Law?
It is the radius from the centre of the field.
What can we say about the force in Coulomb’s Law Equation?
- it is directly proportional to the charge of each particle
- it is inversely proportional to the square of the distance between the particles
What is the charge of a proton?
1.60 x 10 ^-19 C
What does the epsilon (Ɛ) in Coulomb’s Law Equation represent?
Ɛ = permittivity of free space
—– basically what is between the charges
Two balloons are charged with an identical quantity and type of charge: -6.25 nC.
They are held apart at a separation distance of 61.7 cm.
Determine the magnitude of the electrical force of repulsion between them.
F = 9.22 x 10 ^-7 N
Two balloons with charges of +3.37 µC and -8.21 µC attract each other with a force of 0.0626 N.
Determine the separation distance between the two balloons.
r = 1.99 m
Which equation should you use to calculate the electric field strength of a RADIAL field (around a point charge)?
E = k Q/r^2
Which equation should you use to calculate the electric field strength of a UNIFORM field?
E = V/d
What two units are equivalent and can be used for Electric Field Strength?
NC^-1 = Vm^-1
Electric Field strength is a …. .
Vector
What direction would the arrows be if an electric field has a positive charge?
Outwards, as conventionally it is if a positive charge is placed in the field.
What direction would the arrows be if an electric field has a negative charge?
Inwards, as conventionally it is if a positive charge is placed in the field.
During a lightning strike, the Earth’s electric field might be 3000 NC^-1.
Calculate the p.d. between two points on the lightning strike that are 20 m apart.
V = 60,000 V
In the electron beam of a cathode ray oscilloscope, electrons are accelerated through a potential difference of 3000 V, which is set up between parallel plate electrodes that are 3 cm apart.
a) Calculate the electric field strength between these electrodes, assuming it is a uniform field.
b) How much faster will the electrons be moving when they emerge from this field?
c) Explain how the field’s effect would be different if a proton were placed in it.
a) E = 100,000 V m^-1
b) F = -1.6 x 10^14 … a = 1.7563… x10^16 ms^-1 … v = 3.25 x 10^7 ms^-1
c) - Electric Field Strength will remain constant
- The magnitude of the force will remain constant too
- The acceleration will be lower though, due to the mass of the proton being larger
Neutrally charged objects always …
… attract charged objects.
Equipotential lines are …
… link points of the same potential.
What does the density of field lines show?
Strength of field
Uniform field has a …
… constant strength of field throughout
Field lines are …
… lines showing the direction of the field in relation to a positive charge.
As you go further from the centre of the charge …
… the field’s strength decreases (due to the inverse square law).
4 things to remember when sketching Radial Fields;
- Use a ruler
- Make all lines equal in length (by eye)
- Make all lines equally spaced (by eye)
- Use arrows to show the direction a positive charge would move.
a) What force will an electron feel when it is in an X-ray machine’s electron field which has a range of 4.5 x 10^5 Vm^-1?
b) How fast will the electron be travelling if this field accelerates it from rest and it is within the field for a distance of 10 cm?
a) F = -7.2 x 10^-14 N
b) v = 1.26 x 10^8 ms^-1
