A voltage V is applied to the primary coil of a step-up transformer with a 3:1 ratio of turns between its primary and secondary coils. A resistor R connected to the secondary dissipates a power P = 100 W. How much power is dissipated by the same resistor when the ratio of turns in the transformer is changed to 24:1 and the same input voltage is used?

Respuesta :

Explanation:

Let [tex]N_p\ and\ N_s[/tex] are the number of turns in primary and secondary coil of the transformer such that,

[tex]\dfrac{N_p}{N_s}=\dfrac{1}{3}[/tex]

A resistor R connected to the secondary dissipates a power [tex]P_s=100\ W[/tex]

For a transformer, [tex]\dfrac{N_s}{N_p}=\dfrac{V_s}{V_p}[/tex]

[tex]V_s=(\dfrac{N_s}{N_p})V_p[/tex]

[tex]V_s=3V_p[/tex]...............(1)

The power dissipated through the secondary coil is :

[tex]P_s=\dfrac{V_s^2}{R}[/tex]

[tex]100\ W=\dfrac{V_s^2}{R}[/tex]

[tex]V_p^2=\dfrac{100R}{9}[/tex].............(2)

Let [tex]N_p'\ and\ N_s'[/tex] are the new number of turns in primary and secondary coil of the transformer such that,

[tex]\dfrac{N_p'}{N_s'}=\dfrac{1}{24}[/tex]

New voltage is :

[tex]V_s'=(\dfrac{N_s'}{N_p'})V_p'[/tex]

[tex]V_s'=24V_p[/tex]...............(3)

So, new power dissipated is [tex]P_s'[/tex]

[tex]P_s'=\dfrac{V_s'^2}{R}[/tex]

[tex]P_s'=\dfrac{(24V_p)^2}{R}[/tex]

[tex]P_s'=24^2\times \dfrac{(V_p)^2}{R}[/tex]

[tex]P_s'=24^2\times \dfrac{(\dfrac{100R}{9})}{R}[/tex]

[tex]P_s'=6400\ Watts[/tex]

So, the new power dissipated by the same resistor is 6400 watts. Hence, this is the required solution.