Advertisements
Advertisements
प्रश्न
The teachers of Geeta’s school took the students on a study trip to a power generating station, located nearly 200 km away from the city. The teacher explained that electrical energy is transmitted over such a long distance to their city, in the form of alternating current (ac) raised to a high voltage. At the receiving end in the city, the voltage is reduced to operate the devices. As a result, the power loss is reduced. Geeta listened to the teacher and asked questions about how the ac is converted to a higher or lower voltage.
1) Name the device used to change the alternating voltage to a higher or lower value. State one cause for power dissipation in this device.
2) Explain with an example, how power loss is reduced if the energy is transmitted over long distances as an alternating current rather than a direct current.
3) Write two values each shown by the teachers and Geeta.
Advertisements
उत्तर
1) The transformer is a device used for changing the alternating voltage to a higher or lower value. Formation of eddy currents in the iron core of the transformer is one of the causes of power dissipation in this device.
2) In the long-distance transmission of energy through transmission lines, the power loss is mainly due to resistive loss. Now, this resistive loss is proportional to the square of current flowing through the lines i.e
`H prop I^2`
So, to minimise this loss, we need to minimise the current flowing in the wire. In case of dc, if we decrease the current flowing in the wire, though the power losses will decrease but simultaneous power received at the receiving station will also decrease. So, to achieve the required amount of power at the receiving station, we transmit the ac signal by stepping up the voltage with the lower value of current as ac gives the flexibility of stepping up or down the voltage. In this way, the power losses are reduced while maintaining the required amount of power at the receiving station.
3)
Two values shown by the teachers are:
- Believer of giving practical knowledge
- Good explainer
Two values shown by Geeta are:
- Curiosity of learning
- Good listener
APPEARS IN
संबंधित प्रश्न
Derive an expression for e.m.f. and current in terms of turns ratio
Express the turn ratio in terms of voltages.
Mention various energy losses in transformer device
State two factors on which the magnitude of induced e.m.f. depend.
(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.
Explain the working of the transformer.
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 ______.
Magnetic flux passing through a coil is initially 4 × 10-4 Wb. It reduces to 10% of its original value in t second. If the emf induced is 0. 72 mV then t in second is ______.
A 12 V, 60 W lamp is connected to a 220 V AC supply using an ideal transformer. Find the primary current.
