Question

an instrument is marked 180 W ,240 V .if the voltage is lowered to 120 V , what will be its power?
with mathematical representation.​

Answer 1

Answer:-

p = 45 w

Given :-

p = 180 w

V = 220 v

If the voltage is lowered to 120 v

To find :-

The power.

Solution:-

Let's find the resistance of instrument.

The power is given by formula :-

$\huge \boxed {P = \dfrac{v^2}{r}}$

→$180 = \dfrac{240^2}{r}$

→$r = \dfrac{240 \times 240}{180}$

→$r = \dfrac{57,600}{180}$

→$r = 320 \Omega$

Now,

The voltage is decreased to 120v

The voltage is decreased to 120vV = 120 v

→$p = \dfrac{120^2}{320}$

→$p = \dfrac{120\times 120}{320}$

→$p = \dfrac{14,400}{320}$

→$p = 45 w$

hence,

The new power will be 45 watt.