Electric Charges and Fields — Physics STD 12 Science — Question

The introduction of a grid in a triode valve affects plate current by

(a) Making the thermionic emission easier at low temperature

(b) Releasing more electrons from the plate

(c) By increasing plate voltage

(d) By neutralising space charge

A transformer with efficiency 80% works at 4 kW and 100 V. If the secondary voltage is 200 V, then the primary and secondary currents are respectively

(a) 40 A, 16 A

(b) 16 A, 40 A

(c) 20 A, 40 A

(d) 40 A, 20 A

In a head-on elastic collision of two bodies of equal masses:

1. The velocities are interchanged.
2. The speeds are interchanged.
3. The momenta are interchanged.
4. The faster body slows down and the slower body speeds up.
5. All of the above.

The plate current in a diode is zero. It is possible that:

The truth table given in figure represents:

A	B	Y
0	0	0
0	1	1
1	0	1
1	1	1

A star is moving towards the earth with  a speed of 4.5  m/s. If the true wavelength of a certain line in the spectrum received from the star is 5890 Å, its apparent wavelength will be about [c = 3 ]

(a) 5890 Å

(b) 5978 Å

(c) 5802 Å

(d) 5896 Å

Equivalent energy of mass equal to 1 a.m.u. is

(a) 931 KeV

(b) 931 eV

(c) 931 MeV

(d) 9.31 MeV

The frequency and intensity of a light source are both doubled. Consider the following statements.

1. The saturation photocurrent remains almost the same.
2. The maximum kinetic energy of the photoelectrons is doubled.

1. Both A and Bare true.
2. A is true but B is false.
3. A is false but B is true.
4. Both A and B are false.

To make P type semiconductor in silicon :

An inductor, a resistor and a capacitor are joined in series with an AC source. As the frequency of the source is slightly increased from a very low value, the reactance of the.