Electric Fields U4 Flashcards
Why are field lines pointing away from a positively charged particle
Because these lines show the direction a test positive charge would move
Define an electric field
Force acting per init charge
Uniform field : E=
V/d
F/Q
If you double the distance between two plates in a uniform field what happens to the V? Why?
The v=1/2 because of E=V/d ,
They’re inversely proportional
What happens to E when you increase the potential difference between two plates in a uniform field
E increases
What direction do you draw any electric field lines
Away from a positive charge
Towards a negative charge
Why does the E field for a radial field get weaker as you get further away from the charged particle?
Because the field lines are further apart as you move further away from the charged particle therefore the E field is weaker
What is the surface area of a sphere
4(pi)r^2
If you double the radius of a sphere what happens to the surface area? What is this called?
4X larger
Inverse square law
What is E proportional to for a radial field?
1/r^2
Q/r^2
If E is proportional to Q/r^2 then what does E equal?
E=k(Q/r^2)
Where k is a given constant
When does Coulomb’s law apply?
When there are two charged particles in an electric field
If the force Squire’s from Coulomb’s law is negative what does this mean?
It’s an attractive force because the charges are opposite
E=? (Coulomb’s law) and therefore derive F
F=EQ2
KQ1/r^2=F/Q2
KQ1Q2/r^2=F
The Coulomb’s law equation is
F = k Q1Q2/r^2
What is the proportion of forces on two charged particles in an electrical field
They are equal and opposite
What’re the units of electric field strength
N/C
What is the field if the field strength is the same everywhere?
A uniform field
What is E inversely proportional to in a radial field
r^2
What is an experiment to investigate a uniform field?
The oil drop experiment
Describe the oil drop experiment when the circuit is off/on; and what happens when changing the distance and potential difference in the circuit?
1) an atomiser creates a fine mist of oil drops that are charged by friction as they leave the atomiser
2) when the circuit is off the drops fall from the top to the bottom plate due to their weight
3) when the circuit is switched on, the potential difference between the two plates creates a uniform electric field, which exerts a force on the oil drops.
A negatively charged oil drop can be made to float between the two plates by balancing the upward force from the electric field and the downward force of the oil drops weight.
4) if you increase the potential difference the electric field strength will increase and the oil drop will wove towards the positive plate
5) if you increase the distance between the two plates or decrease the potential difference then the field strength is reduced therefore the oil drop will fall to the bottom plate due to it’s weight being a larger force.
