Question

1.) What is the reading shown by the ammeter when the switch is open ?
2.) When the switch is closed, what is the equivalent resistance of the circuit ?
3.) When the switch is closed, what is the new ammeter reading ?​

Answer 1

Answer:

1) When switch S is open total current through ammeter.

i = 20/(3+2) = 4A.

when switch is closed i = 20/(3+1) = 5A.

2) When the switch is closed, the R2 resistance essentially becomes a non-factor and you have less resistance, which would mean you would have higher current.

3) Any current flowing in a wire has some inductance. Larger the current larger the inductance. Also inductance will be higher in highe voltage. Known as EMF or Electro Motive Force is the theory behind Motors and Transformers. In a closed circuit, the ammeter typically contains a high grade circular magnetic material. Like transformers instead of one block of material the circular block will have many thin slices of circular materials bound together. This will reduce eddy currents flowing in the material. when you open and clasp the ammeter, the circular magnetic material will pick up the inductance amplifies them to a voltage that drives the meter. Higher the current, higher the voltage. Thus you can get fairly accurate reading of current flowing in a closed circuit.

Note that there is not enough inductance for this to work on lower voltages or lower current. In those instances you connect your ammeter in series to measure.

By the way magnetic material used in transformers and ammeters are Cold Rolled Grain Oriented Steel which provides high flux density.

Step-by-step explanation:

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Answer 2

2)What is the equivalent resistance of the circuit when the switch is open and closed?

If you did the math correctly, the equivalent resistance across A & B when the switch is closed is 8 Ohms

3)What happens to the reading on the ammeter when the switch is closed?

When the switch is closed, resistors R1 and R2 are in parallel, so that the total circuit resistance is smaller than when the switch was open. As a result, the current increases.