PHY101 Short Notes Set 2

PHY101 Short notes

Q1. Define charge density

When the charges are continuously over a region-a line, the surface of a material, or inside a sphere-we must specify the charge density. Depending upon how many dimensions the region has, we define: (a) For linear charge distribution: dq ds (b) For surface charge distribution: dq dA (c) For volume charge distribution: dq dv The dimensions of are determined from the above definitions.

Q2. Define Gauss’s Law?

Answer: The total electric flux leaving a closed surface is equal to the charge enclosed by the surface divided by  .We can expressed in mathematics form

enclosed q E d A

Q3. Define electric potential?

Answer: The electric potential is the energy of a unit charge in an electric field. So in our MKS units the unit of potential is 1Joule/Coulombs=1Volt. Another useful unit is 1Electron Volt.

Q4. Define 1Ev?

Answer: One electron-volt=enrgy gained by moving one electron charges through one volt.

1.6 10 1.6 10 x C x V x J It is useful to note that

Kev eV Mev eV Gev eV

Q5. Given a system of charges, we can always compute the force - and hence the potential - That arises from them. Here are some important general statements:

1. Potentials are more positive in regions which have more positive charge.
2. The electric potential is a scalar quantity (a scalar field, actually).
3. The electric potential determines the force through F=− du/dr, and hence the electric

Field because F= qE. d) The electric potential exists only because the electrostatic force is conservative

Q6. Define Capacitor?

Answer: Two conductors isolated from one another and from their surroundings, from a capacitor. These conductors may be of any shape and shape, and at any distance from each other. If a potential difference is created between the conductors (say, by connecting the terminals of a battery to them), then there is an electric field in the space between them. The electric field comes from the charges that have been pushed to the plates by the battery. The amount of charge pushed on to the conductors is proportional to the potential difference between the battery terminals (which is the same as between the capacitor plates). Hence Q V  . To convert this into equality, we write Q

CV

. This provides the definition of capacitance,

Q · C · V

Q7. Define Ampere?

Answer: Electric current is the flow of electrical charge. If a small amount of charge dq flows in time dt, then the current is

dq · i · dt

. If the current is constant in time,

then in time t, the current that flows is q

i x t

. The unit of charge is ampere, which is defined as:

Coulombs · ampere · Second

A car’s battery supplies up to 50 amperes when starting the car, but often we need to deal with smaller values:

miliampere · ma · A · microampere · A · A · nanoampere · nA · A · picoampere · pA · A

Q8. Define Resistance?

Answer: Resistance is directly proportional to the voltage V and inversely proportional to the current I.

V · R · I