Starting Electronics

Measuring

current

and

voltage

Figure

3.14 A

circuit v/hich

is

used

to

show

the

effect

of the

meter's

own

resistance

in a

circuit

if

you

don't

believe it!). But when you apply your multi-

meter across resistor R2 you find that the voltage

indicated is only about 3 V.

The

fact

is that when the multi-meter is not connected

to the circuit the voltage is 4.5 V, but as soon as the multi-

meter is applied, the voltage across resistor R2 falls to

3 V.

Also,

the voltage across resistor Rl

rises

to 6 V (both

voltages must add up to the battery voltage, remember).

Applying the multi-meter affects the operation of the

cir-

cuit, because the multi-meter resistanc ...