Electricity — Class 10 Science PYQs

S.I. unit of electrical resistivity is

The maximum resistance of a network of five identical resistors of $\frac{1}{5}\Omega$ each can be -

Study the I-V graph for three resistors of resistances $R_1$, $R_2$ and $R_3$ and select the correct statement from the following :

The minimum resistance which can be made using five resistors each of resistance $10\Omega$ is :

(A) Show how you would connect three resistors each of resistance $6\Omega$, so that the combination has a resistance of $9\Omega$. Also justify your answer.
OR
(B) In the given circuit calculate the power consumed in watts in the resistor of $2\Omega$ :

Use Ohm's law to determine the potential difference across the $3\Omega$ resistor in the circuit shown in the following diagram when key is closed :

Use Ohm’s law to determine the potential difference across the $3\Omega$ resistor in the circuit shown in the following diagram when key is closed :

(i) Name two safety measures commonly used in electric circuits and appliances.
(ii) The power rating of an electric oven is $220$ V; $2$ kW. If it is used in a domestic electric circuit of current rating of $5$A, what result do you expect ? Justify your answer with necessary calculations.

(A) (i) State whether the currents and potential difference in all the bulbs will be same or different when in a circuit three bulbs of :
(a) same wattage are connected in series.
(b) same wattage are connected in parallel.
(c) different wattage are connected in series.
(d) different wattage are connected in parallel.

(ii) Two identical resistors of $24\Omega$ each are connected to a battery of $6\text{ V}$. Calculate the ratio of the power consumed by the resulting combinations with (a) minimum resistance and (b) maximum resistance.

OR

(B) Draw a schematic diagram of a circuit consisting of a battery of six $2\text{V}$ cells, a $6\Omega$ resistor, a $12\Omega$ resistor and a $18\Omega$ resistor and a plug key all connected in series. Calculate the following (when key is closed) :
(i) Electric current flowing in the circuit.
(ii) Potential difference across $18\Omega$ resistor.
(iii) Electric power consumed in $18\Omega$ resistor.

(A) (i) Define electric power. Express it in terms of potential difference ($V$) and resistance ($R$).
(ii) An electric oven is designed to work on the mains voltage of $220$ V. This oven consumes $11$ units of electrical energy in $5$ hours. Calculate :
(a) power rating of the oven
(b) current drawn by the oven
(c) resistance of the oven when it is red hot
OR
(B) (i) Write the relation between resistance $R$ and electrical resistivity $\rho$ of the material of a conductor in the shape of cylinder of length $l$ and area of cross-section $A$. Hence derive the SI unit of electrical resistivity.
(ii) The resistance of a metal wire of length $3$ m is $60\Omega$. If the area of cross-section of the wire is $4\times 10^{-7}{\text{ m}}^2$, calculate the electrical resistivity of the wire.
(iii) State how would electrical resistivity be affected if the wire (of part 'ii') is stretched so that its length is doubled. Justify your answer.