Refraction

Use of transformers

Transformer Effect 

V_in = N_p             or         V_out = N_s

V_out     N_s                            V_in         N_p

1. A step down transformer reduces voltage from 240 V (V_in) to 6 V.  If there are 1000 turns on the primary windings (N_p),  how many are there on the secondary windings ?

V_out = N_s               6V/240V = N_s/1000   N_s/1000 = 0.025      N_s = 1000 x 0.025 = 25 turns

 V_in         N_p

2. A step down transformer reduces voltage from 240 V (V_in) to 12 V (V_out).  If N_p = 200 turns calculate  N_s.

V_out = N_s            12V/240v = Ns/200 Ns = 12/240 x 200 = 10 turns

V_in         N_p

3. A transformer has 1000 turns on it’s primary windings and 100 in the secondary . If V_in is in 20V calculate V_out.

V_out = N_s            V _out/20v = 100/1000  V_out= 20 (100/1000) = 2 V

V_in         N_p

4.  In a transformer N_p = 2000 turns and N_s = 50 turns.  If V_in =400 V, calculate V_out.

V_out = N_s            V _out/400v = 50/2000  V_out= 400 (50/2000) = 10 V

V_in         N_p

5.  A step up transformer increases voltage from 4 V to 40 V.  If N_p = 100 turns calculate N_s.

V_out = N_s            40V/4v = Ns/100 Ns = 40/4 x 100 = 1000 turns

V_in         N_p

6.  A step down transformer reduces voltage from 100 V to 10 V.  If N_p = 2000 turns calculate N_s.

V_out = N_s            10V/100v = Ns/2000 Ns = 10/100 x 2000= 200 turns

V_in         N_p

7.  In a transformer N_s = 10 turns and N_p = 500 turns.  If V_out = 10 V calculate V_in.

            V_in/V_out = N_p/N_s rearranging V_in = V_outN_p/N_s  V_in = 10(500/10) = 500V

8.  If N_s = 40 turns and Np = 4000 turns calculate V_in if V_out = 10 V.

V_in/V_out = N_p/N_s rearranging V_in = V_outN_p/N_s  V_in = 10(4000/40) = 1000V

Mock Exam