Advertisements
Advertisements
प्रश्न
The line that draws power supply to your house from street has ______.
- zero average current.
- 220 V average voltage.
- voltage and current out of phase by 90°.
- voltage and current possibly differing in phase `phi` such that `|phi| < pi/2`.
पर्याय
b and c
a and d
b and d
a and c
Advertisements
उत्तर
a and d
Explanation:
Alternating currents are used for household supplies, which are having zero average value over a cycle.
The line is having some resistance, so power factor `cos phi = R/Z ≠ 0`
So, `phi = pi/2 ⇒ phi < pi/2`
i.e., phase lies between 0 and `pi/2`.
Important point: The average value of alternating quantity for one complete cycle is zero.
The average value of ac over half cycle (t = 0 to T/2)
`I_(av) = (int_0^(T/2) i dt)/(int_0^(T/2) dt) = (2i_0)/pi = 0.637i_0` = 63.7% of i0
Similarly `V_(av) = (2V_0)/pi` = 0.637 V0 = 63.7% of V0.
APPEARS IN
संबंधित प्रश्न
State the principle on which transformer works.
Name two factors on which the magnitude of an induced e.m.f. in the secondary coil depends.
Complete the following sentence :
……… energy is converted into …………energy by an electric motor.
For what purpose are the transformers used? Can they be used with a direct current source?
The transformer is used in ______ current circuits.
Describe, with the help of a suitable diagram, the working principle of a step-up transformer. Obtain the relation between input and output voltages in terms of the number of turns of primary and secondary windings and the currents in the input and output circuits.
State the principle of a step-up transformer. Explain, with the help of a labeled diagram, its working ?
Describe briefly and two energy losses, giving the reasons for their occurrence in actual transformers ?
What is a transformer? On what principle does it work?
Can a transformer be used with direct current source? Give reason.
State the factors on which the frequency of the alternating e.m.f. depends.
Name three losses of energy in a transformer. How are they minimized?
(i) Draw a clear labelled diagram of an electric bell.
(ii) Explain in brief, its working.
(iii) What material is used for the core of an electric bell? State the reason.
A transformer is essentially an a.c. device. It cannot work on d.c. It changes alternating voltages or currents. It does not affect the frequency of a.c. It is based on the phenomenon of mutual induction. A transformer essentially consists of two coils of insulated copper wire having different numbers of turns and wound on the same soft iron core.
The number of turns in the primary and secondary coils of an ideal transformer is 2000 and 50 respectively. The primary coil is connected to a main supply of 120 V and secondary coil is connected to a bulb of resistance 0.6 Ω.
Power in primary coil is ______.
Electrical energy is transmitted over large distances at high alternating voltages. Which of the following statements is (are) correct?
- For a given power level, there is a lower current.
- Lower current implies less power loss.
- Transmission lines can be made thinner.
- It is easy to reduce the voltage at the receiving end using step-down transformers.
The self-inductance of a closely wound coil of 200 turns is 10 mH. Determine the value of magnetic flux through the cross-section of the coil when the current passing through the coil is 4 mA.
The primary coil of a transformer has 60 turns whereas its secondary coil has 3000 turns.
If a current of 5A flows in the primary coil, how much current will flow in a load in the secondary coil? State the assumption you have made regarding the transformer, in this calculation.
An ideal transformer converts 170 V a.c. to 1.70 KV a.c. to transmit a power of 3.4 KW. If primary coil has 500 turns then alternating current in secondary coil is ______.
