Mean Value

Q. If an ac main supply is given to be 220 V. What would be the average e.m.f. during a positive half cycle

1. 198V
2. 256V
3. None of these
4. 386V

Q. 1) An electron emitted by a heated cathode and accelerated through a potential difference of $2.0KV,$ enters a region with uniform magnetic field of $0.15T.$ Dtermine the trijectory of the electron if the field is trannsverse to its initial velocity?

2) An electron emitted by a heated cathode and accelerated through a potential difference of $2.0KV,$ enters a region with uniform magnetic field of $0.15T.$ Dtermine the trijectory of the electron if the field makes an angle of ${30}^{\circ }$ with the initial velocity?

Q. A constant voltage of 25 V is applied to a series L – R circuit at t = 0, by closing a switch. What is the potential difference across the resistor and the inductor at time t = 0?

1. 0 V, 25 V
2. 12.5 V, 12.5 V
3. 10 V, 15 V
4. 25 V, 0V

Q. An ideal choke takes a current of $10A$ when connected to an ac supply of $125V$ and $50Hz$. A pure resistor under the same conditions takes a current of $12.5A$. If the two are connected to an ac supply of $100V$ and $40Hz$, then the current in series combination of above resistor and inductor is

1. $10/\sqrt{2}A$
2. $20A$
3. $10A$
4. $12.5A$

Q. A resistance of $20\Omega$ is connected to a source of alternating current rated $110V,50Hz$. Then the time taken by the current to changes from its maximum value to the r.m.s. value is

1. $2.5\times {10}^{-3}sec$
2. $2.5\times {10}^{-5}sec$
3. $5\times {10}^{-3}sec$
4. $2.5\times {10}^{-4}sec$

Q. Alternating current can not be measured by dc ammeter because average value of current for complete cycle is zero.

1. True
2. False

Q. If an AC main supply is given to be 220 V. The average emf during a positive half cycle will be

1. 198 V
2. 220 V
3. $220\sqrt{2}V$
4. 240 V