Science (English Medium) Class 12 - CBSE Question Bank Solutions

The activity R of an unknown radioactive nuclide is measured at hourly intervals. The results found are tabulated as follows:

1. Plot the graph of R versus t and calculate the half-life from the graph.
2. Plot the graph of ln `(R/R_0)` versus t and obtain the value of half-life from the graph.

What can be the causes of helical motion of a charged particle?

The following figure shows the input waveforms (A, B) and the output waveform (Y) of a gate. Identify the gate, write its truth table and draw its logic symbol.

The Earth's magnetic field at the Equator is approximately 0.4 G. Estimate the Earth's magnetic dipole moment. Given : Radius of the Earth = 6400 km.

Write the truth table for the combination of the gates shown. Name the gates used.

Identify the logic gates marked 'P' and 'Q' in the given circuit. Write the truth table for the combination.

You are given the two circuits as shown in following figure. Show that circuit

1. acts as OR gate while the circuit
2. acts as AND gate.

(a)

(b)

Write the truth table for a NAND gate connected as given in the following figure.

Hence identify the exact logic operation carried out by this circuit

You are given two circuits as shown in following figure, which consist of NAND gates. Identify the logic operation carried out by the two circuits.

(a)

(b)

Write the truth table for circuit given in figure below consisting of NOR gates and identify the logic operation (OR, AND, NOT) which this circuit is performing.

(Hint: A = 0, B = 1 then A and B inputs of second NOR gate will be 0 and hence Y=1. Similarly work out the values of Y for other combinations of A and B. Compare with the truth table of OR, AND, NOT gates and find the correct one.)

Write the truth table for the circuits given in following figure consisting of NOR gates only. Identify the logic operations (OR, AND, NOT) performed by the two circuits.

(a)

(b)

An iron ring of relative permeability µ_r has windings of insulated copper wire of n turns per meter. When the current in the windings is I, find the expression for the magnetic field in the ring.

Give the truth table and circuit symbol for NAND gate

Draw logic symbol of an OR gate and write its truth table. 

Answer the following question :

Distinguish between digital and analogue signals.

A triangular loop of wire placed at abc is moved completely inside a magnetic field which is directed normal to the plane of the loop away from the reader to a new position a'b'c'. What is the direction of the current induced in the loop? Give reason.

In the given circuit diagram a voltmeter ‘V’ is connected across a lamp ‘L’. Ho would (i) the brightness of the lamp and (ii) voltmeter reading ‘V’ be affected, if the value of resistance ‘R’ is decreased? Justify your answer.

A 10 V battery of negligible internal resistance is connected across a 200 V battery and a resistance of 38Ω as shown in the figure. Find the value of the current in circuit.

A 5 V battery of negligible internal resistance is connected across a 200 V battery and a resistance of 39Ω as shown in the figure. Find the value of the current in circuit.

You are given a circuit below. Write its truth table. Hence, identify the logic operation carried out by this circuit. Draw the logic symbol of the gate it corresponds to.