Question

13.why do u connect an ammeter in series and voltmeter in parallel in a circuit?

Answer 1

Ammeter has a very low resistance. It has a very low potential drop across its terminals when current flows through it . To measure amount of current accurately it is always connected in series so that there is very minimal change in current when ammeter is connected in series and it causes very low voltage drop in circuit.
 Voltmeter is always connected in parallel and it measures voltage drop across its terminal. It has a very high resistance so that very small amount of current flows through it when connected in parallel and there is no change on readings measured by the voltmeter.    

Answer 2

Ammeter:-

An ammeter is just a converted Galvanometer and measures the current flowing through the circuit by showing proportional deflection. An ammeter is formed by connecting a Galvanometer with a low resistance in parallel.

$\bigstar$So the Ammeter is connected in series with the circuit elements and measures the current flow in a circuit.

Voltmeter:-

A Voltmeter is also a converted Galvanometer which measures the amount of Voltage (or) in other words the potential difference accross two points in a circuit. A voltmeter is formed by connecting a Galvanometer in series with a high resistance.

$\bigstar$So the Voltmeter is attached in parallel in a circuit and measures the voltage in a circuit.