Two resistors `400Omega` and `800Omega` are connected in series with a `6V` battery. It is desired to measure the current in the circuit. An ammeter of `10Omega` resistance is used for this purpose figure. What will be the reading in the ammeter? Similarly, if a voltmeter of `10,000Omega` resistance is used to measure the potential difference across the `400Omega` resistor, what will be the reading in the voltmeter?

Explanation

The circuits are shown in figure.
In figure, all the resistors are in series,
`:.` total resistance of the circuit,
`R=400+800+10=1210Omega`
Hence, current in the circuit,
`I=V/R=(6)/(1210)=0*00496A`
Reading in ammeter is `0*00496A`
In figure, the resistors of `400Omega` and `10,000Omega` are in parallel, their effective resistance `R_p` will be
`R_p=(400xx10,000)/(400+10,000)=(5000)/(13)Omega`
`:.` Total resistance of the circuit
`=(5000)/(13)+800=(15400)/(13)Omega`
Current in the circuit,
`I_1=(6)/(15400//13)=(39)/(7700)A`
Potential difference across A and B
`=I_1R_p=(39)/(7700)xx(5000)/(13)=(150)/(77)=1*95V`
`:.` Reading of voltmeter is `1*95V`