# Homework Help: NEVER connect an ammeter in parallel ->WHY?

1. Jul 22, 2007

### hiyoo89physics

"NEVER connect an ammeter in parallel!!!" -->WHY?!

Why must an ammeter never be connected in parallel, or across the terminals of a power source?

All I know about this is that you'll blow a fuse if you connect an ammeter in parallel... but I don't know why you'd blow a fuse.

My guess: The current that you'd measure if the ammeter was connected in series would be the current that had gone through the resistor, so the current would be lower than the current coming straight out of the power supply. This un-resisted (?) current is too high for the ammeter to bear.

If you could help me on this, I'd be so grateful! THANK YOU!

2. Jul 22, 2007

### Moridin

If you hook up an ammeter in series, it measures the entire current through the circuit. If you hook it up parallel to it, it will not experience the entire current through the circuit but only a fraction of it.

The more stuff you put in series, the higher the combined resistance will get.

3. Jul 22, 2007

### Astronuc

Staff Emeritus
Because an ammeter has low 'resitance/impedance'. It is designed to measure the current. A high impedance would reduce the current and add a voltage drop.

Placing an ammeter in parallel produces a 'short circuit' and the resulting current will 'blow a fuse'.

Conversely, a voltmeter has a high impedance and is placed in parallel.

4. Jul 22, 2007

### ank_gl

when does a fuse blow up??
because of the heavy current.
when you put an ammeter in parrallel, you are reducing the resistance of the circuit(ammeter has very low resistance).
low resistance = high current = blown fuse