Question

Question 10 - M1 (18 marks) Many people use electric kettles in their houses to boil water (for example to make a cup of tea or coffee) These devices work by passing an electric current through a metal wire. As the electricity passes through the wire, it gets hot and this is the source of heat to boil the water. Consider the Kettle shown in the figure below. The electricity passes through a coiled 'resistance wire' which is housed within a sheath for safety purposes. It is this resistance wire that does the heating On-Off switch Steel Alloy Sheath Insulation Heating element Resistance Wire Enlarged view of heating element highlighting resistance wire A typical kettle contains a coiled resistance wire that is 23.50m long and 1.20mm in diameter. These wires are made of Nichrome (a mix of 80% Nickel and 20% Chromium. 10.1) (5 marks) If this kettle is connected to a 240V mainss outlet, what is its Power output? P = 10.2) (5 marks) If this kettle is filled with 2 Litres of water taken from the tap at 15C, what is the minimum time required to boil the water? 10.3) (2 marks) Strictly speaking, the coiled resistance wire will change size when it is heated. What is the length and diameter of the resistance wire at the temperature when the water boiling? L= d= 10.4) (6 marks) On a single plot of resistivity on the y-axis versus temperature on the x-axis plot how you would expect i) the resistivity of Nichrome metal (Ni-20%Cr) to change as you change temperature ii) the resistivity of Pure Nickel to change as you change temperature ii) the resistivity of a Nickel-20% Aluminium alloy to change as you change temperature The x-axis should start at 0OK. Both axes should be drawn with linear scales and the curves should be clearly labelled resistivity temperature

Answer 1

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Tepenatune coffcind Nichnome : 0.000t / R:Ro (+a A7) = 31.156 (1 + 0.000 4 8S 3a.2152 Nao YA Volume rtemains Same u9ine a'L' a.L L': d.658979,/05 ALso sprifie ran's fonce doy not chonpe R'e' 37.2157 a' 31.156 23.5 a -6 1.13/47104 a this Solniy we R0087932. 82- a 2.658979 Y10 0087932.82 2 2 2 21007 mt

esistvrity () Nickel (Ni20t, AL) Nichrom 7Tempec) 100