why 108 questions

I need an explanation for this Physics question to help me study.

• Two identical steel balls mounted on wooden posts initially have different amount of charge as follows. The balls are allowed to touch and then are separated again. What’s the final charge on each ball in each case?
  a) one +3 mC and the other +15 mC
  b) one +12 mC and the other – 4 mC
• One positive charge and one negative charge, each of magnitude 4×10^-6C, are located a distance of 0.1 m from each other.
  a) What’s the magnitude of force exerted on each charge?
  b) On a drawing, indicate the direction of the forces acting on each charge.
  c) Draw electric field lines between two charges.
• A charge of 30 C passes at a steady rate through a resistor in a time of 5 s. What’s the current through the resistor?
• Two identical light bulbs are connected to a battery with electromotive force of 9 V. Each light bulb has resistance of 10 W. 1) If the two light bulb connected in series,
  a) please draw the circuit and calculate the total resistance and current in the circuit;
  b) please calculate voltage drop on each resistor.
  2) If the two light bulb connected in parallel,
  a) please draw the circuit and calculate the total resistance and current in the circuit;
  b) please calculate current going through each resistor.
• Why do the lighting system in your building have parallel circuits instead of series circuits?