Advertisements
Advertisements
Question
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`.
Options
b and c
a and d
b and d
a and c
Advertisements
Solution
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
RELATED QUESTIONS
Explain the construction and working of the transformer.
Find the ratio of primary and secondary currents in terms of turn ratio in an ideal transformer.
How much current is drawn by the primary of a transformer connected to 220 V supply when it delivers power to a 110 V − 550 W refrigerator?
Which coil of a step up transformer is made thicker and why?
Explain why an induced current must flow in such a direction so as to oppose the change producing it.
How are the e.m.f in the primary and secondary coils of a transformer related with the number of turns in these coils?
Given the input current 15 A and the input voltage of 100 V for a step-up transformer having 90% efficiency, find the output power and the voltage in the secondary if the output current is 3 A.
Draw a labeled diagram of a full wave rectifier circuit. State its working principle. Show the input-output waveforms ?
In an ideal transformer, an output of 66 kV is required when an input voltage of 220 V is available. If the primary has 300 turns, how many turns should the secondary have?
What is the ideal transformer?
Can a transformer be used with direct current source? Give reason.
What are step-up and step-down transformers?
Give the advantage of AC in long distance power transmission with an illustration.
A transformer having efficiency of 80% is working on 200 V and 6 kW power supply. If the current in the secondary coil is 6 A, the voltage across the secondary coil and the current in the primary coil respectively are ____________.
Define a Transformer.
A step-down transformer connected to an ac mains supply of 220 V is made to operate at 11 V, 44 W lamp. Ignoring power losses in the transformer, what is the current in the primary circuit?
For an LCR circuit, the power transferred from the driving source to the driven oscillator is P = I2Z cos φ.
- Here, the power factor cos φ ≥ 0, P ≥ 0.
- The driving force can give no energy to the oscillator (P = 0) in some cases.
- The driving force cannot syphon out (P < 0) the energy out of oscillator.
- The driving force can take away energy out of the oscillator.
A transformer consisting of 300 turns in the primary and 150 turns in the secondary gives output power of 2.2 kW. If the current in the secondary coil is 10 A, then the input voltage and current in the primary coil are ______.
