**Aim:-**Measurement of the high resistance by using loss of charge method.

**Apparatus**

**:-**Multimeter –1no

Ammeter-(0-200ma)-1no

Voltmeter –(0-30v)-1no

Capacitor-10uf-1no

Resister-100K-1no

Power supply-(0-30v)-1no

.

**Circuit Diagram:-**

**Observation Table:**-

S.

NO.

Time (sec) V(without

R)

V(with R) Log10(V/v)

without R

Log10(V/v)

with R

**Theory:-**

In this method the resistance which is measured is connected in parallel with

the capacitor C and the electronic voltmeter V. The capacitor is the charged up to some

suitable voltage by means of the battery having the voltage V and is then allowed to

discharge through the resistance.

The terminal voltage is observed over the considerable period of the time

during discharge.

Let ,

V=initial voltage on the charged capacitor .

.v=instantaneous discharging voltage.

I=the discharging capacitor current through the unknown resistor at time “t”.

Q=the charge still remaining in the capacitor.

I=dq/dt=-cdv/dt since[I=V/R]

V/R+C dv/dt=0 (1)

1/RC dt+1/V.dV=0

integrating both sides

t/RC+logev+K=0 (2)

K is const. of integration

At initial condition

When T=0 , v=V from equ. (2)

K=-logeV

now equ. (2) becomes

t/RC+logev-logeV=0

therefore. Loge (v/V)=-t/RC

v/V=e-t/RC

v=V*e-t/RC

Taking log on both sides

logev=logeV+logee-t/RC

R=t/C*loge(V/v)

R=0.4343*t/C*log10(V/v)

Procedure:-

1) Connections is make as per the circuit diagram.

2) Close the switch s and keep s2 open the capacitor charge by own leakage method.

3) New open reading and voltmeter .as its own resistance.

4) Note down the reading of the voltmeter

**Vs**equal interval of the time**Result:-**High resistance of the resistance is calculated by using loss of charge method.

**Viva Questions**:- 1)Why this method is called as loss of charge method?

2)What errors occur while performing this practical?