Help with questions please

[jonnymc11]

i still cant get this one!

Q2. Calculate the power dissipated by resistor 2 in the circuit here

(R1 = 5, R2= 10, supply voltage = 20v)

If in series then add resistors together ( giving Rt) and divide answer into voltage, this gives your current = 1.333 A

P = I x I x R

So P = 1.333 x 1.333 x 10 = 17.76 W

i cant get 1.33, i get 0.75

15/20 = 0.75 ?

 

[Atty]

Rt=R1+R2

Rt=5+10

Rt=15ohms

I=Vs/Rt

I=20/15

I= 1.3A

 

[jonnymc11]

sorted!

 

[jonnymc11]

29. When a semi conductor diode is connected across an a.c. supply having a peak value of 5 V, the peak inverse voltage across the diode is: a) 2.5 V B) 3.5 V c) 7.07 V d) 10 V

how? general rule?

thanks chaps!

 

[Andy™]

29. When a semi conductor diode is connected across an a.c. supply having a peak value of 5 V, the peak inverse voltage across the diode is: a) 2.5 V B) 3.5 V c) 7.07 V d) 10 V how? general rule?

thanks chaps!

peak inverse voltage is 10v, not 7.07

more info

 

[jonnymc11]

. A single-phase circuit dissipates 2.5 kW of power and operates at a power factor of 0.95. The current flowing in the circuit will be:

a) 11.4 A B) 10.32 A c) 10.8 A d) 10.4 A

ALSO IS THIS CORRECT?

The voltage supplied to the primary winding of an ideal step down transformer is 1000V and the output voltage is 400V. If the secondary current is 20A the value of the primary current will be:

a) 50 A B) 25 A c) 10 A d) 8 A

1000/400 = 2.5

20/2.5 = 8

 

[jonnymc11]

http://www.electricianforum.co.uk/301answers.pdf

says 7.07 mind

 

[jonnymc11]

I dont no how to do the following question...

A single-phase circuit dissipates 2.5 kW of power and operates at a power factor of 0.95. The current flowing in the circuit will be:

a) 11.4 A B) 10.32 A c) 10.8 A d) 10.4 A

ALSO IS THIS CORRECT, i have tried it myself?

The voltage supplied to the primary winding of an ideal step down transformer is 1000V and the output voltage is 400V. If the secondary current is 20A the value of the primary current will be:

a) 50 A B) 25 A c) 10 A d) 8 A

1000/400 = 2.5

20/2.5 = 8