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`.
विकल्प
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
The primary coil of an ideal step-up transformer has 100 turns and the transformation ratio is also 100. The input voltage and power are 220 V and 1100 W, respectively. Calculate the
(a) number of turns in secondary
(b) current in the primary
(c) a voltage across secondary
(d) current in secondary
(e) power in secondary
Name two factors on which the magnitude of an induced e.m.f. in the secondary coil depends.
Why is the core of a transformer laminated?
Complete the following sentence :
……… energy is converted into …………energy by an electric motor.
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.
Can a transformer be used with direct current source? Give reason.
Name three losses of energy in a transformer. How are they minimized?
Draw a labelled diagram to show the various parts of a step-up transformer and step down transformer.
The power supply to the primary coil of a transformer is 200 W. Find
(i) Current in primary coil if the e.m.f. supply to it is equal to 220V.
(ii) The number of turns in the primary coil is equal to 80 and that in secondary is 800. What is the transformation ratio?
(iii) Name the type of transformer.
(iv) What will be the output voltage?
(v) What is the current in the secondary coil for an ideal transformer?
(vi) What is the output power?
(vii) Is output and input power equal?
(viii) Compare the current flowing in a secondary coil and in a primary coil.
Transformer works on ______.
Mention the various energy losses in a transformer.
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 ____________.
Read the following paragraph and answer the question:
Long distance power transmissions
The large-scale transmission and distribution of electrical energy over long distances is done with the use of transformers. The voltage output of the generator is stepped up. It is then transmitted over long distances to an area sub-station near the consumers. There the voltage is stepped down. It is further stepped down at distributing sub-stations and utility poles before a power supply of 240 V reaches our homes.
Which of the following statement is true?
A transformer is used ______
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?
A 60 W load is connected to the secondary of a transformer whose primary draws line voltage. If a current of 0.54 A flows in the load, what is the current in the primary coil? Comment on the type of transformer being used.
The primary coil of a transformer has 60 turns whereas its secondary coil has 3000 turns.
If a 220 V ac voltage is applied to the primary coil, how much emf is induced in the secondary coil?
How do the input and output powers in a transformer compare? State the assumption made.
