CBSE Std-12 Science Physics — Practice Paper

A cell of EMF 2 V and internal resistance 0.5 Ω is connected to an external resistance of 3.5 Ω. The terminal voltage of the cell is:

Assertion (A): An ammeter must have very low resistance. Reason (R): An ammeter is connected in series and should not affect the current in the circuit. Choose the correct answer: A) Both A and R are true; R is the correct explanation of A B) Both A and R are true; R is not the correct explanation of A C) A is true but R is false D) A is false but R is true

A convex lens of focal length 20 cm forms a real image 4 times the size of the object. The object distance is:

Assertion (A): A concave mirror always produces a real image. Reason (R): A concave mirror converges all light rays falling on it. Choose the correct answer: A) Both A and R are true; R is the correct explanation of A B) Both A and R are true; R is not the correct explanation of A C) A is true but R is false D) Both A and R are false

The power dissipated in a resistor is 10 W when connected to a 10 V supply. If the same resistor is connected to a 20 V supply, the power dissipated is:

The refractive index of a material is 1.5. The critical angle for total internal reflection at the material-air interface is approximately:

Assertion (A): The resistance of a metal conductor increases with increase in temperature. Reason (R): The number of free electrons in a metal decreases with increase in temperature. Choose the correct answer: A) Both A and R are true; R is the correct explanation of A B) Both A and R are true; R is not the correct explanation of A C) A is true but R is false D) A is false but R is true

A magnifying glass held 5 cm from a small object produces a virtual image at 25 cm from the lens (on the same side as the object). The focal length of the lens is:

The EMF of a cell is greater than its terminal voltage when:

Which of the following optical devices primarily uses the principle of total internal reflection?

Two resistors of resistances 2 Ω and 3 Ω are connected in series to a battery of EMF 5 V. Calculate the current in the circuit. (Neglect internal resistance)

A plane mirror is placed 10 cm in front of an object. Describe the nature of the image formed. List any two characteristics of the image.

State Ohm's law. A wire of resistance 5 Ω is subjected to a potential difference of 10 V. Calculate the current flowing through the wire.

A cell of EMF 1.5 V and internal resistance 0.5 Ω is connected to an external circuit containing a resistance of 2.5 Ω. Calculate (i) the current in the circuit, and (ii) the terminal voltage of the cell.

Define electromotive force (EMF). Why is the terminal voltage of a cell less than its EMF when current is drawn from it? Explain with an equation.

A convex lens forms a real image of height 4 cm from an object of height 2 cm placed at a distance of 30 cm from the lens. Calculate the focal length of the lens.

Derive the lens formula. Also define magnification and write the relationship between magnification and object/image distances.

Three resistors of 1 Ω, 2 Ω, and 3 Ω are connected in parallel. Calculate the equivalent resistance of the combination.

State and explain Kirchhoff's first and second laws. Give one practical application of these laws.

A ray of light traveling in air (refractive index = 1) enters a medium of refractive index √3. For what angle of incidence will the refracted ray be perpendicular to the reflected ray?

Explain total internal reflection. Derive the expression for critical angle. State the conditions necessary for total internal reflection.

Explain how a battery (cell) with internal resistance supplies current to an external circuit. Derive the expressions for: (i) the current in the circuit, (ii) the terminal voltage, and (iii) the power dissipated in the internal resistance. Also discuss energy conservation in this process.

State and derive the expressions for resistivity and resistance of a conductor. Explain how resistivity varies with temperature. Describe the mechanism behind this variation. What is the difference between resistivity and conductivity?

Derive the lens formula for a convex lens using ray geometry. Explain the sign convention used. Also derive the expression for magnification. Use this to show the relationship between object distance, image distance, and focal length.

Explain the phenomenon of total internal reflection. Derive the expression for critical angle. Why does light bend away from the normal when traveling from a denser to a rarer medium? How is this principle applied in optical fibers?

A student sets up a circuit to verify Ohm's law using a wire, an ammeter, a voltmeter, a variable power supply, and connecting wires. (i) Draw and label the circuit diagram showing proper connections of the ammeter and voltmeter. (ii) State the precautions to be taken while performing this experiment. (iii) If the wire has resistance 5 Ω and is connected to voltages of 2 V, 4 V, and 6 V successively, predict the currents obtained. (iv) How would the graph of V vs I appear? What does the slope represent?

A student observes that when light from a laser pointer traveling through air hits a glass block at a certain angle, it undergoes total internal reflection inside the glass. (i) Explain what is meant by total internal reflection. (ii) The refractive index of glass is 1.5. Calculate the critical angle for glass-air interface. (iii) If light hits the glass at an angle of incidence of 60° (from air into glass), will it emerge from the other side or undergo total internal reflection? Show calculations. (iv) State one practical application of total internal reflection in optical devices.