Elements of electric toasters and electric irons are made of an alloy rather than a pure metal. Give two reasons to justify the statement.

$(a)$ What do the following symbols represent in a circuit? Write the name and one function of each.
$(b)$ Draw a schematic diagram of a circuit consisting of a battery of $12 \, V$,three resistors of $5 \, \Omega$,$10 \, \Omega$,and $20 \, \Omega$ connected in parallel,an ammeter to measure the total current through the circuit,and a voltmeter to measure the potential difference across the combination of resistors.
$(c)$ State any one advantage of connecting electrical devices in parallel with the mains instead of connecting them in series in a household circuit.

Study the $V - I$ graph for a resistor as shown in the figure and prepare a table showing the values of $I$ (in amperes) corresponding to four different values of $V$ (in volts). Find the value of current $I$ (amperes) for $V=10$ volts. How can we determine the resistance of the resistor from this graph?

Define resistance of a conductor. State the factors on which resistance of a conductor depends. Name the device which is often used to change the resistance without changing the voltage source in an electric circuit.
Calculate the resistance of $50 \, m$ length of wire of cross-sectional area $0.01 \, mm^2$ and of resistivity $5 \times 10^{-8} \, \Omega \, m$.

$A$ piece of wire having resistance $R$ is cut into four equal parts. $(a)$ How will the resistance of each part compare with the original resistance? $(b)$ If the four parts are placed in parallel,how will the joint resistance compare with the resistance of the original wire?

$(a)$ How much current will an electric bulb draw from a $220 \ V$ source,if the resistance of the bulb filament is $1200 \ \Omega$?
$(b)$ How much current will an electric heater coil draw from a $220 \ V$ source,if the resistance of the heater coil is $100 \ \Omega$?