Time taken by a 836 W heater to heat one litre of water from $10^{\circ}\text{C}$ to $40^{\circ}\text{C}$ is

JEE Main · 2004 · 24 Apr 2004 · Offline · Heat & Thermodynamics

Time taken by a 836 W heater to heat one litre of water from

1 0^{\circ} C

4 0^{\circ} C

(A)50 s
(B)100 s
(C)150 s✓ Correct
(D)200 s

Answer: (C)

Solution

The litre of water, taken as

1000

g with specific heat

4.18

J per gram per degree, needs heat

Q = m c Δ T = 1000 \times 4.18 \times (40 - 10) = 1.254 \times 1 0^{5}

J to warm from

1 0^{\circ}

C to

4 0^{\circ}

C. A heater rated at

836

W delivers

836

J every second, so the time required is

t = \frac{Q}{P} = \frac{1.254 \times 1 0 ^{5}}{836} = 150

JEE Main · 2004 · 24 Apr 2004 · Offline · Single correct option

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