Question

1. How can a neutral item be attracted to a charged object? Devise a test that will tell you whether the ball was neutral or positive. You can use any tools, even something not in your lab kit.

2. Your mother told you never to remove toast from a toaster with a metal knife. Did you listen? Let's say for a moment that you didn't. Which are you more likely to survive, being in parallel with the toaster wires or being in series? Explain.

3. Voltages are always measured between two points. Why?

4. If you wish to store a large amount of energy in a capacitor bank, would you connect capacitors in series or parallel? Explain.

Answer 1

1] Neutral atoms get attracted to a charged object through induction. When a charged object is near them, it induces a partial charge of the opposite kind near the charged object and it is this which causes the attraction. To test whether the ball is neutral or positive, introduce a plastic measuring ruler rubbed with your hair in front of the ball. The hair gives the ruler a partial positive charge and so if the ball is positive, it will get repelled else it is neutral.

2] Being in series is less dangerous since the voltage drop across the toaster will be large and so not enough voltage will pass through your body. If in parallel, the voltage drop across the toaster and your body will be the same and so the current passing through you will be fatal.

3] Voltage decreases in series and so voltage must be measured between two points in a connection. Also, since the voltage in parallel circuits are same, the voltage between these two points will be the same as the voltage measured.

4] Energy stored in a capacitor is given by: U = (1/2)CV²

in series: 1/C_eq = 1/C₁ + 1/C₂ + ....

in parallel: C_eq = C₁ + C₂ + ....

Capacitors in parallel have an equivalent capacitance which is greater than the individual capacitances (unlike in the series case) and so to store a large amount of energy, the capacitors must be connected in parallel.