Electricity — Class 10 Science PYQs

(a) The resistance of a wire of $0.01\mathrm{cm}$ radius and $1.0\mathrm{cm}$ length is $7\Omega$. Calculate its resistivity.
OR
(b) An electric heater is rated $220\mathrm{V}$; $11\mathrm{A}$. Calculate the power consumed if the heater is operated at $200\mathrm{V}$.

(a) (i) Due to change in length and area of cross-section of a conductor, resistance of conductor changes while resistivity does not change. Why ?
(ii) Conductors of electric toasters and electric iron are made of an alloy rather than a pure metal. Why ?
(iii) Define the S.I. unit of electric current.
OR
(b) (i) How many bulbs of resistance $8\Omega$ each should be connected in parallel combination to draw a current of $2\mathrm{A}$ from a battery of $4\mathrm{V}$ ?
(ii) Name the device used for measuring electric current. How is it connected in a circuit ?
(iii) State Joule's law of heating.

(a) A wire of resistance $R$ is cut into three equal parts. If these three parts are then joined in parallel, calculate the total resistance of the combination so formed.
OR
(b) Define electric power. When do we say that the power consumed in an electric circuit is $1\mathrm{watt}$ ?

Consider the following electric circuit :
Calculate the values of the following :
(a) The total resistance of the circuit
(b) The total current drawn from the source
(c) Potential difference across the parallel combination of $10\Omega$ and $15\Omega$ resistors

(a) Write the relationship between resistivity and resistance of a cylindrical conductor of length $l$ and area of cross-section $A$. Hence derive the SI unit of resistivity.
(b) Why are alloys used in electrical heating devices ?

(a) Consider the following circuits :
In which circuit will the power dissipated in the circuit be (I) minimum (II) maximum ? Justify your answer.
OR
(b) Two lamps, rated $100\mathrm{W}$; $220\mathrm{V}$ and $60\mathrm{W}$; $220\mathrm{V}$ are connected in parallel to electric main supply of $220\mathrm{V}$. Find the current drawn by the two lamps from the supply.

(a) Define one ampere.
(b) The resistance of a wire of $0.01\mathrm{cm}$ radius is $14\Omega$. If the resistivity of the material of the wire is $44\times 10^{-8}\Omega \mathrm{m}$, find the length of the wire. (Given $\pi =\frac{22}{7}$)

(a) Consider two lamps A and B of rating $50\mathrm{W}$; $220\mathrm{V}$ and $25\mathrm{W}$; $220\mathrm{V}$ respectively. Find the ratio of the resistances of the two lamps (i.e. $R_A:R_B$).
OR
(b) Heat produced per second due to a current in a resistor of $4\Omega$ is $400\mathrm{joules}$. Calculate the potential difference across the resistor.

(a) Define one volt potential difference between two points in an electric field.
(b) Draw a schematic diagram of an electric circuit of a cell of $1.5\mathrm{V}$, $5\Omega$ and $10\Omega$ resistor and a plug key, all connected in series. Calculate the current drawn from the cell when the key is closed.

An electric bulb is connected to a power supply of $220\mathrm{V}$. If the current drawn by the bulb from the supply is $500\mathrm{mA}$, the power of the bulb is :