Answer:
Transformers are used to increase or decrease the voltage of AC currents
Explanation:
A transformer is a device consisting of two coils (called primary and secondary coil) wrapped at the two sides of a soft iron core. When an AC current is present in the primary coil, it induces a magnetic field inside the core, and the presence of this changing magnetic field induces a voltage (and a current) into the secondary coil.
The voltages in the primary and the secondary coil are related by the transformer equation:
where
Vp, Vs are the voltages in the primary and secondary coil
Np, Ns are the number of turns in the primary and secondary coil
There are two types of transformers:
- Step-up transformers: these have 
, so that 
, which means that they increase the voltage. They are used to increase the voltage of the AC current produced by the power plants, before being sent into the transmission lines.
- Step-down transformers: these have 
, so that 
, which means that they decrease the voltage. They are used at the end of the transmission lines, before the houses, in order to decrease the voltage and allow the household appliances to work properly (in fact, household appliances need lower voltages to work)
The actual position of the object is <span>at a great distance, effectively infinite. The other options given in the question are not at all correct. The correct option among all the options that are given in the question is the last option or option "D". I hope that this answer has actually come to your great help.</span>
I believe the correct answer is C all the other options seem funny to me
Answer:
η = 2.57%
Explanation:
Given:
Output power of the steam power plant, P(out) = 200 MW
Consumption of coal, m = 700 tons/h = (700 × 10³)/3600 kg/s= 194.44 kg/s
Heating capacity of the coal, Cv = 40000 kJ/kg
now,
Input power, P(in) = mCv
or
P(in) = 194.44 kg/s × 40000 = 7777.77 MW
thus,
efficiency, η = P(out)/P(in) = (200 MW) / (7777.77 MW) = 0.02571
or
η = 2.57%
Answer:
VR=2
Explanation:
driven=60
driving=30
but VR=driven/driving
VR=60/30
VR=2
hence the velocity ratio VR is 2
