Electricity Practice Questions for CBSE - Ohm’s Law

1. What is value of resistance for an ideal voltmeter and ammeter? S; It is infinity for voltmeter and 0 for the ammeter
2. Define electric potential? Amount of work done to move a unit charge from infinity to any point in the electric field of a given charge
3. Why is an ammeter connected in series in a circuit? Ammeter has very low resistance, hence to measure the amount of current flowing through the circuit; it must pass through the ammeter hence it is connected in series
4. 4.Why is a voltmeter connected in parallel in a circuit? Voltmeter posse’s very high resistance, to find potential across given resistance, the minimum current must pass through the voltmeter and maximum through the resistance
5. State the law that governs the strength of the current passing through a metallic conductor when a p.d is applied across its end. Illustrate this law graphically? Ohm’s law is the law. It provides linear relation between current and voltage
6. State the law which governs the amount of heat produced in a metallic conductor when current is passed through it for a given time. Express this law mathematically? Joules heating effect is the law that provides heat produced according to it H = I²Rt
7. Define resistance. What are the factors on which it depends? Obstruction possessed by the conductor in the flow of current is called resistance, it depends on the length, area, temperature, nature of the material.
8. A copper wire of resistivity P is stretched to reduce its diameter to half its previous value. What is the new resistivity? Resistivity is independent of dimension so it will remain P (no change)
9. Define the S I unit of electric current and potential difference. Current =Ampere, Potential difference = Volt
10. What is an expression for equivalent resistance when we connect them in series? R= R+R+R... (in parallel combination)
11. What is an electric fuse? Explain its function. To prevent the circuit from excess current, we have an electric fuse that consists of high resistance and low melting point it will melt when a high current flows through it.
12. What do you mean by a shunt? It is a small value of resistance that is connected in parallel with the galvanometer
13. Can we increase or decrease the range of the ammeter? We can increase the range by connecting suitable resistance in parallel 1
14. Is Ohm’s law is universal? No, it is not accepted universally. There are many nonohmic devices also which does not follow ohm’s law
15. Name 2 non Ohmic devices. Semiconductor and electrolytes
16. Is ohm’s law valid for high temperature? No as with temperature, resistance changes so Ohm law not valid
17. What is the need of Kirchoff's law? Ohm’s law is applicable only on small circuits so to solve complex circuits we need Kirchhoff's law.
18. What is the unit of resistivity Ohm-meter?
19. Is there any vector form of Ohm's law? Yes. We express it in terms of current density, conductivity, and electric field J=σE
20. Have you ever heard about negative resistance? Yes in material like GaAs, in a particular region When we increase voltage-current decreases then they said to posses negative resistance.

Electricity Practice Questions for CBSE: Meter Bridge

1. What is the principle of MB? Wheat Stone bridge
2. What happens at the balancing point No current flows through the galvanometer
3. Why no current flows through the galvanometer? It is because there is no potential difference, for the flow of current potential difference must be there.
4. Any other instrument based on Wheat stone bridge Post office box, Carey foster
5. Why Constantan and Manganin are used to make standard resistance Low-temperature coefficient and high resistivity
6. The resistivity of a wire depends on the Material of the wire, temperature
7. A toaster produces more heat than a light bulb which has greater resistance H is inversely proportional to R when connected in parallel so the light bulb has greater resistance
8. When is the Wheatstone bridge most sensitive When all four P, Q, R, and S are of the same magnitude
9. Why Wheat stone bridge is not suitable for very low resistance Due to end resistance measurement is not perfect
10. What happens if the galvanometer and cell interchanged at the balance point. The balance point remains unchanged.

Electricity Practice Questions for CBSE: Potentiometer Internal resistance and comparison of emf

Assuming that the student was assigned the experiment “To determine the internal resistance of a primary cell (which can not be recharged) using potentiometer“

1. Examiner (E): What was the experiment allotted to you? Students(S): Sir, I was assigned the experiment to determine the internal resistance of a primary cell using a potentiometer.
2. Examiner (E): OK, Tell me the principle of a potentiometer S: Sir. The principle of a potentiometer is that the potential drop across any length of a wire of uniform cross-section and composition and carrying a constant current is directly proportional to the length.
3. Examiner (E): Good. What is internal resistance? S: The resistance offered by the electrodes and electrolytes of a cell is called internal resistance.
4. 4.E: What are the factors affecting internal resistance? S: Sir. The internal resistance of a cell depends on the nature of electrodes and electrolyte, the temperature of the electrolyte, the area of electrodes, the concentration of electrolyte, and the distance between electrodes.
5. Examiner (E): Good; how does the internal resistance change if we increase the area of electrodes? S: Sir, the internal resistance will decrease if we increase the area of electrodes.
6. Examiner (E): What will happen to internal resistance if we increase the temperature? S: The internal resistance of the cell will decrease with an increase in temperature.
7. Examiner (E): How does the Resistance of a conductor vary with temperature? S: For a conductor, the resistance increases with an increase in temperature due to the decrease in relaxation time.
8. Examiner (E): Which one is a common cell out of daniel and Leclanche S: Laclanche cell We generally use it in dry form.
9. Examiner (E): Why we prefer Leclanche cell S: Because of its cost. Danial cell is costly.
10. Examiner (E): Define the potential gradient of a potentiometer. S: The potential drop per unit length of the potentiometer wire is called a potential gradient.
11. Examiner (E): How does the sensitivity of a potentiometer vary with a potential gradient? S: The sensitivity of the potentiometer decreases with an increase in potential gradient.
12. Examiner (E): Can you explain why? S: As the potential gradient increases, a greater potential difference is obtained for a small change in the length of the wire. Or the length of the potentiometer for a given change in potential will be less. The potentiometer is more sensitive if we get a considerably larger change in length for a given change in potential. Therefore, with an increase in potential gradient, the sensitivity decreases.
13. Examiner (E):v OK can we draw any amount of current from a primary cell? What limits the value of current drawn? No, we can not draw any amount of current from a cell. The internal resistance of the cell limits the maximum value
14. Examiner (E): What are the defects of the primary cells? S primary cell is the cell which we can not recharge its main defects are Local action and Polarisation
15. Examiner (E): What is the role of CuSO₄ in Daniel cell S: it acts as a depolariser
16. Examiner (E): Then what is depolariser in Leclanche cell? S: MnO₂
17. Examiner (E): Why in the primary circuit we should not use a primary cell? S: It cannot provide steady current through the wire for a long time
18. Examiner (E): Which potentiometer would you select 4 wire or 10 wire? S: 10 wire because it is more sensitive and having less potential gradient.
19. Examiner (E): What are the characteristics of the wire of the potentiometer? S: Uniform area, high resistivity, low-temperature coefficient
20. Examiner (E): OK you are a really good student last question. it is generally said, the electric current should not pass through the potentiometer wire for a long time, Why S; sir this will heat up the potentiometer wire and it will change its resistance. the potential gradient will change

Electricity Practice Questions for CBSE: SEMICONDUCTOR PRACTICAL PN Junction

Suppose you are assigned P-N Junction

1. Examiner (E): What are you doing? S; Sir I am finding the relation between current and voltage for P-N junction in forward and reverse bias
2. Examiner (E): OK, what is a P-N junction? S; P-N junction is a semiconductor device in which a P-type semiconductor is joined with an N-type semiconductor
3. Examiner (E): What is depletion layer? S: It is a thin region around the junction that is free from holes and electrons
4. Examiner (E): Good, can you explain to me how we can join two semiconductors, is there any specific way? S: Yes sir we have various ways by which we can join P-type semiconductor with N-type such as grown junction diode, fuse junction diode.
5. Examiner (E): What is ideal junction diode S: Ideal junction diode is that which conduct only in forward bias
6. Examiner (E): Good, Tell me why it is so that current is flowing so easily in forward bias whereas not so easily in reverse bias S; sir in forward bias depletion region is thin so resistance is low hence current flow due to majority carrier whereas in reverse bias depletion region is thick so resistance is so high hence no current flow due to majority carrier current only flow due to minority carrier
7. Examiner (E): Is the P-N junction is the ohmic device? S; No it is non-ohmic devices; current is not vary linearly with potential.
8. Examiner (E): What is knee voltage/ S; Sir knee voltage is that below which graph in forward bias is non –linear or non-ohmic and above which it is linear or ohmic.
9. Examiner (E): Which elements are used as intrinsic semiconductors S; Si and Ge are used as semiconductors. It is because it has four electrons in its valance shell and forms a covalent bond
10. Examiner (E): Carbon also has four electrons in a valance shell then why it is not used as a semiconductor? S; Electricity can conduct through carbon, but carbon does have significant resistance, and much of the electrical energy will be lost as heat energy when it passes through carbon and it forms diamond crystal structure so when we add impurity atoms it will not make any significant change...+ Carbon is not used as semiconductor it has 4 valence electrons in its valence shell but the energy gap is very small it will conduct electricity even at room temperature, the size of carbon is very small. It depends upon the structure of carbon. In the case of germanium and silicon, they have d orbits in the outer shell and they have greater mobility.
11. Examiner (E): Tell me various types of P-N junctions S: P-N junction is also called diode, such as a photodiode, light-emitting diode, tunnel diode, Zener diode, varactor diode, etc.
12. Examiner (E): What is the value of the potential barrier of a silicon and germanium S; 0.7V and 0.3 V
13. Examiner (E): What is the difference between P-N diode and Zener Diode S: Zener is highly dopped and works in reverse bias
14. What is Zener breakdown? S; When a very high reverse voltage is applied across a semiconductor diode, a large amount of current flows through it. This effect is called Zener breakdown.
15. What is a charge on P type or N-type semiconductor? S: it is charge less
16. What is donor impurity? S: The pentavalent impurity atoms like Sb, As
17. What is acceptor impurity? S: The trivalent impurity like B, Al
18. What is dopping? S: Addition of impurity to pure semiconductor 19.
19. How does the conductivity of semiconductors vary with temperature? S; The conductivity of the semiconductor increases with time
20. Why a large electric current flows, the semiconductor gets damaged S: It is because it gets heated
21. What are two important processes involved in the formation of a P-N junction S; Diffusion and Drift, when a PN junction is formed due to concentration gradient, the holes diffuse from P side to N side, and electron diffuse from the N side to the P side. The drift of charge carriers occurs due to the electric field due to built-in potential barrier an electric field directed from n region to P region is developed across the junction. This field causes motion of electron on p side to n side and motion of holes on n side to p side thus a drift current start which is opposite to diffusion current.

Practice Questions for CBSE: Optics Experiments Convex lens, Prism, Travelling Microscope

1. Define refractive index. It is defined as the ratio of the velocity of light in rarer medium to velocity in a denser medium
2. What is the least value of refractive index possible? One
3. What can you infer if someone says that he has a medium of refractive index less than one? Through that medium light travel faster than its speed through a vacuum
4. Define focus. The point on the principal axis at which the parallel rays after reflection/refraction converge or appear to converge
5. Define the pole of a spherical mirror. The center of the curved and reflecting surface of a spherical mirror
6. Define optic center. It is the geometrical center of the lens.A ray of light passing through this point does not suffer any deviation.
7. What is the type of lens in an air bubble formed inside water Convex lens
8. Is your eye is a lens? It is a convex lens
9. What is the focal length of a lens? The distance between the principal focus and the optical center of a lens is called the focal length of the lens
10. How will you distinguish between a plane mirror, concave mirror, and a convex mirror without feeling its surface with your hand?
11. What is the linear magnification of plane mirrors, concave mirrors, and convex mirrors? It is 1 for plane more than 1 for concave and less than 1 for convex
12. What are the differences between the convex lens and concave lens? A concave lens has diverging property and convex converging Concave is thin at the middle whereas convex thick
13. What is dispersion? The phenomenon of splitting white light into its constituent colors on passing through a glass prism is called dispersion of light.
14. Why a glass slab does not produce dispersion whereas a prism does? Since a rectangular glass slab is equivalent to two similar prisms placed with their base inverted.the dispersion and deviation produced by the two prisms are equal but in the opposite direction so net deviation and dispersion are zero.
15. Define the refractive angle of the prism. It is the angle between two refracting surfaces
16. What is parallax? It may be defined as the relative shift between the two objects placed at different distances from the eye when the eye is moved to and fro.
17. What is index correction? It is a difference between observed distance and actual distance because of sharpe edges of the needle
18. How is parallax removed? By making two objects coincident
19. Which color of light shows maximum deviation. Violet
20. In which situation, a convex lens behaves as a concave lens? When a convex lens is placed in a medium of refractive index greater than that of the material of the lens
21. In an equilaterial prism if the incident angle is 45^º then the minimum deviation is 30^º
22. Distinguish real image and virtual image. The image which can be obtained on a screen is real which can't is virtual.
23. If red, green, and blue light incident on right angle prism. If only one light will not suffer TIR then what will be that light It will be Red
24. The color of sky is blue due to which optical phenomenon Scattering
25. Dispersion is due to Change in velocity and Wavelength
26. Define the power of a lens. It is the ability of a lens to converge a beam of light towards its principal axis.
27. Define angle of deviation. It is the angle between the incident ray and emergent ray
28. What are the factors on which the lateral displacement produced by a glass slab depends?
29. Which type of lens has negative power? Concave
30. Which lens is called a diverging lens? Concave
31. What is the angle of minimum deviation? It is the angle at which the angle of incidence becomes equal to the angle of emergence so that the ray of light will be parallel to the base of the prism
32. What is the cause of dispersion? Different colors travel with different velocities when passes through the prism
33. Does the refractive index depend on wavelength? Yes the refractive index depends on the wavelength of light inversely proportional
34. What happens to a prism if it is placed in water? It will remain unchanged
35. Why travelling microscope is called so? A Travelling microscope is called so because it can be moved in horizontal and vertical directions to take measurements while seeing the magnified image of the object under study. It can be used to determine the diameter of the capillary tube, to determine the refractive index of the material of a glass slab by measuring real depth and apparent depth, etc.
36. When water is filled on the concave mirror, then how will it behave? It will behave as a plano-convex lens.
37. What type of eye-piece is used in a traveling microscope? Ramsden’s eyepiece.
38. What is the role of lycopodium powder on the upper surface of the glass slab while determining refractive index by traveling microscope? So that we can focus over the surface of the glass slab.
39. What is the SI unit of the refractive index? It has no unit.

Practice Questions for CBSE: Half Deflection Method

1. What are you doing? I am finding the resistance of a galvanometer by half deflection method and its figure of merit.
2. What is a moving coil galvanometer? It is a device used to detect the direction as well as the magnitude of the electric current.
3. What is the principle of moving coil galvanometer? Current carrying coil placed in a magnetic field experience torque.
4. What is the figure of merit? Amount of electric current required to produce one scale deflection in the galvanometer
5. Define the current sensitivity. The deflection produces per unit current through it
6. What is the nature of the magnetic field in the moving coil galvanometer? It is a radial magnetic field.
7. Out of the galvanometer voltmeter and ammeter which one has maximum and minimum resistance? An ammeter is having a minimum and voltmeter maximum in fact ideal ammeter is having zero and a voltmeter is having infinite resistance
8. Which type of galvanometer you are using? It is a moving coil Watson type galvanometer
9. Why this practical is known as a half deflection? It is because when we connect the shunt, half of the current flows through the galvanometer and half through shunt
10. What will be the approximate value of the resistance of the galvanometer? It is near to the value of shunt
11. What is the importance of the radial magnetic field in a moving coil galvanometer Radial magnetic field makes the arm of the couple fixed hence the torque on the coil is always the same in all positions so that we get the linear scale.
12. Why ammeter is connected in series So that whole of the current passes through it
13. Why voltmeter is connected in parallel So that it draws very small current 14.Why ammeter has low resistance As we connect shunt so effective resistance of the circuit is minimum and maximum current flows through it.