Electrical Engineering - Transformers - Discussion

Discussion :: Transformers - General Questions (Q.No.4)

4. 

If a transformer has 50 turns in the primary winding and 10 turns in the secondary winding, what is the reflective resistance if the secondary load resistance is 250 ?

[A]. 250
[B]. 25
[C]. 6,250
[D]. 62,500

Answer: Option C

Explanation:

No answer description available for this question.

Bhagyashree said: (Dec 12, 2010)  
R2=250

k=n1/n2=50/10
R1=R2*k^2
=250*(2500/100)
R1=6250ohm

Hjhgjk said: (Dec 21, 2010)  
K=N2/N1
N1=50
N2=10
K=(10/50)=1/5
SECONDARY TO PRIMARY R/K^2
SO 250/(1/5)^2=250*25=6250 OHMS

Prakash. D. said: (Feb 9, 2011)  
Turns ratio K= n1/n2= 50/10
K=5,
w.k.t..., R1/R2=K^2
R1=250*25
R1=6250 ohms.

Chintan said: (Apr 25, 2011)  
N1=50 , N2=10
Turn ratio K=N2/N1=10/50
K=1/5=0.2
now,R2/R1=K^2
R1=R2/K^2
=250/0.2^2
R1=6250 ohms.

Siddu said: (May 30, 2011)  
Turns ratio will proportional to square of load then square of resistance in sec/pri 2n square.

Pinnapareddy .Sandhya Lakshmi said: (Jun 27, 2011)  
r1=r2/k^2
k=n2/n1=10/50=1/5
r2=250
r1=250/(1/5)^2=6250
r1=6250

Divij said: (Jun 29, 2011)  
r1=(n1/n2)^2*r2

WHERE n1=50 , n2=10,r2=250

Ans: 6250

Sanjeev Kr. Rajoria said: (Sep 7, 2011)  
Transformation ratio a = N1/N2
so
a=50/10=5
now
load resistance referred to primary= (a^2)*(load resistance)
so
the reflected load = 5^2*250
= 25*250
= 6250 ohm
So the correct ans is (c)= 6250 ohm

Kuldeep Bisht said: (Oct 9, 2011)  
Primary resistence R'=R2/(K)2

here k=N2/N1=10/50=0.2
hence R'=250/0.2*0.2=6250 Ohm

Amit Ranjan said: (Oct 11, 2011)  
Eqv.resistance referred to primary=r1+r2/(k*k)

Here r1 is not given

k=10/50=1/5

Hence ans = 250/(1/25) = 6250 ohm.

Sunil Gorga said: (Nov 15, 2011)  
v1i1=v2i2
v1*v1/r1=v2*v2/r2
(v1/v2)^2=r1/r2
we know n1/n2=v1/v2
so (50/10)^2=r1/250
r1=250*5=6250

Anil said: (Jan 23, 2012)  
Resistance matching R1=(n1/n2)^2*rL
hence, r1=(50/10)^2*250
= 25*250
=6250 ohm

Mahendra Chauhan said: (Mar 20, 2012)  
# given data primary coil turns=50,secondary coil turns=10 & secondary load 250 ohm.

#equation N=secondary coil turns/primary coil turns
(Rpri=reflected in to primary)
Rpri=(1/n)^2*RL
so N =10/50
=0.2
Rpri =(1/0.2)^2*250

=(5)^2*250
=25*250
=6250.

Mahendra Dhakchavle said: (Apr 15, 2012)  
R2=250

k=n1/n2=50/10
R1=R2*k^2
=250*(2500/100)
R1=6250ohm

Kalyan said: (May 10, 2012)  
Rs=250
I1^2Rs=I2^2Rf
(I1/I2)^2*Rs=Rf
From Transformation ratio N2/N1=I1/I2=K
(50/10)^2*250=Rf
25*250=Rf
Rf=6250ohm

Sunil Keshari said: (May 27, 2012)  
N1=50
N2=10
R2=250 ohm
K=(N2/N1)
(R2/R1)=K^2
(250/R1)=(10/50)^2
R1=(2500*250)/100
R1=6250 ohm

Nidhi M J said: (Jun 10, 2012)  
Copper losses produced by r2 in primary side must be same as that in secondary side.
I1^2*r2'=I2^2*r2
R2'= (I2/I1) ^2*r2
Where I2/I1=N1/N2.

Virendra Ranpise said: (Aug 23, 2012)  
Resistance ratio=R2/R1
Xmer ratio(K)=N2/N1
Where,
R1=Primary winding resistance
R2=secondary winding resistance
N1=Primari winding turns
N2=secondary winding turns
FORMULA FOR CALCULATING R1
R2/R1 = K square
i.e. R2/R1 = (N2/N1)square

250/R1 = (10/50) square
So
R1 = (250) / ((10/50) square)
R2=6250 ohm

Akshat Gupta said: (Aug 31, 2012)  
Where
n1=50
n2=10
r2=250ohm
so
resistance matching r1= (n1/n2)^*rl
hence,
r1=(50/10)^2*250
=25*250
=6250 ohm

S.Anjineyulu Naik said: (Oct 1, 2012)  
Turn ratio, k=N2/N1.

=10/50.

=1/5=0.2.

Actual resistance in secondary circuit is R2=250 ohm's.

Reflective resistance means, the secondary resistance referred to primary winding is,

R2'=R2/k^2.

=250/ (0.2) ^2.

=250/0.04.

=6250 ohm's.

Mallikarjun said: (May 24, 2013)  
R2' = r2/(kxk).
r2 = 250 ohms.

k = n2/n1 = 0.2.
(kXk) = 0.04.

R2' = 250/0.04 = 6250.

Yatish Ahire said: (Jun 1, 2013)  
Primary resistance R1 = R2/(K)2.

Here,

K = N2/N1 = 10/50 = 0.2.

Hence,

R' = 250/0.2*0.2 = 6250 Ohm.

Ododo said: (Jun 12, 2013)  
Please am confused, turns ratio is it the same as transformer ratio?

I saw that turns ratio = N2/N1, and I still saw that turns ratio = N1/N2, which one is correct with proofs please.

Engr. Mamoona Akbar said: (Jan 17, 2014)  
t2/t1 = sqrt (load impedance/source impedance).

10/50 = sqrt (250/x).

0.2*0.2 = 250/x.

x = 250/0.04.

x = 6250.

Eshan Mishra said: (Feb 16, 2014)  
There is difference b/w the terms if simply turn ratio, voltage ratio is mention and transformation ratio is mention in the question.

Eg:- transformation ratio is k, k=[V2/V1=N2/N1=I1/I2].

Simple turn ratio, voltage ratio is equal to 1/k
N1/N2, V1/V2.

And there is one more important relation,
(V2/V1)=Square root(R2/R1).

Arun Kumar Raju C said: (Apr 4, 2014)  
Ns/Np = sqrt(load resistance/source resistance).

Akash.Bhure said: (Apr 29, 2014)  
Solution:

No.of turns in the primary(N1) = 50.

No.of turns in the secondary(N2) = 10.

Turns ratio(K) = N2/N1 = 10/50 = 0.2.

Secondary load resistance(R2) = 250 Ohm.

Reflective resistance(R1) = R2/K^2.

(R1) = 250/(0.2)^2.
(R1) = 250/0.04 = 6250 ohm's.

Sandip Chhatrola said: (Aug 31, 2014)  
K^2 = R2/R1.

1/25 = 250/R1.

R1 = 6250 ohm.

Bhawana Singh said: (Aug 19, 2015)  
Turn ratio will proportional to square of load then square of resistance in secondary upon primary 2n square.

Rudra said: (Aug 24, 2015)  
What will be the Phasor diagram for it?

Santosh Murkut said: (Mar 24, 2016)  
The transformation ratio is said that N2/N1 = V2/V1 = I1/I2 = K.

Hence,

1) A resistance R1 in primary become K^2 * R1 when transferred to the secondary.

2) A resistance R2 in secondary become R2 / K^2 when transferred to the primary.

Therefore,

R1 = 250 / (10/50)^2 = 6250 ohm.

Vyankatesh Badgujar said: (Nov 14, 2016)  
N1= 50 , N2 = 10.

Turn ratio K = N2/N1 = 10/50,
K = 1/5 = 0.2,
Now, R2/R1 = K^2.

R1 = R2/K^2,
= 250/0.2^2,
R1 = 6250 ohms.

Sandeep Kumar said: (Jan 8, 2017)  
N2/N1= Sq.rt(R2/R1)
10/50 = Sq.Rt(250/R1)
(1/5)^2 = 250/R1.
R1=250*25 = 6250.

Arjun said: (Jan 16, 2017)  
Reflective resistance = {(1/k^2)*Rload}.

Rocky said: (Mar 1, 2017)  
Transformation ratio is N2/N1. Am I right?

Faisal said: (Jun 17, 2017)  
The Formula is this, R1=(N1/N2)^2 RL.
and R1 is given, N1 is given, N2 is given,
So, 250=(50/10)^2 RL.
250 = 25 RL.
Therefore, RL = 250 * 25 = 6250.

Tom said: (Jul 31, 2017)  
Here, n2/n1=r1/r2.

Paul said: (Aug 28, 2017)  
Ododo is the only one making sense here.
k = turns ratio = N2/N1 (This is most often the conclusion based on the 20mins I've spent on the web researching this).

Sumit said: (Sep 26, 2017)  
If primary side 1000 turn and 1000 watt on primary side find out secondary side pawer in watt if seconady turn 100.

Tutun Mondal said: (Dec 27, 2017)  
K=N2/N1=1/5.

SECONDARY TO PRIMARY R1=R2/K^2 =250/(1/5)^2=250*25=6250OHMS.

Abhishek Mohapatra said: (Jan 7, 2018)  
From the basics:

You have to find what resistance on primary will have similar effect as 250 on secondary.
in ideal transformer power associated with primary equals secondary hence V2^2/250 = v1^2/Rreq. similarly V2*I2 =V1*I1. if you know what voltages are related in the same way as a number of turns i.e V2/V1 = N2/N1 then you can easily relate all currents and impedances.

Vaibhav said: (Apr 8, 2018)  
Can I find reflected impedance or turns ratio if the only efficiency of the transformer is provided?

Majid Mahmood said: (Aug 19, 2019)  
According to my calaculation:

v1i1 = v2i2
v1*v1/r1 = v2*v2/r2
(v1/v2)^2 = r1/r2.

We know n1/n2 = v1/v2
so (50/10)^2 = r1/250 => 25 = r1/250,
r1 = 250 * 25 = 6250.

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