# kinetic energy of electron in electric field

#### shenno

hi
i am stuck on the question in the image i have attached, I am unsure of how to go about the question.
the principles i am trying to use:
conservation of energy for the electron
so ki+ui=kf+uf
where k is the kinetic energy and u is the potential energy of the electron,
The electron does positive work moving upwards against gravity.
The electron will loose potential energy in moving closer to the positive charged plate.
I am not sure how to work out the change in potential energy of the electron.

#### studiot

Your first job is to distinguish between the potential energy due to the gravitational field and the PE due to the electric field.

ki+ui=kf+uf
What are these ?

• topsquark

#### shenno

Your first job is to distinguish between the potential energy due to the gravitational field and the PE due to the electric field.

What are these ?
ki=kinetic energy of electron initially= 2x10^-15 joules
kf=kinetic energy of electron finally is what we are looking for.
ui/uf=potential energy of electron initially/finally . I am not sure how to work this out?
I guess you have to use the information of the potential difference of 120.9kv
I am aware of the formula u=qV where u is the electric potential energy, q is the charge and V is the voltage.
so does ui=(1.602x10^-19)(120.9x1000)=1.936818x10^-14 ?

#### shenno

Your first job is to distinguish between the potential energy due to the gravitational field and the PE due to the electric field.

What are these ?
the work done against gravity must equal the change in potential energy. I am not sure how to calculate the potential energy though of the electron initially and finally.