Tag: electrical fuse and mcb

Questions Related to electrical fuse and mcb

An electric iron draws a current of 15 A from a 220 V supply. What is the cost of using iron for 30 min everyday for 15 days if the cost of unit (1 unit $=$ 1 k W hr) is 2 rupees?

physics electric current and its effects electric fuse electrical fuse and mcb fuse

  1. Rs. 49.5

  2. Rs. 60

  3. Rs. 40

  4. Rs. 10

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Correct Option: A
Explanation:

$I=15 A, V=220 V, t=30 min$
$Energy=P\times t=VIt$
$=220\times 15\times \frac {30}{60}\times 15$
$=3300\times \frac {1}{2}\times 15 W hr$
$=3.3\times kW\times 7.5 hr$
$=24.75 kW hr$
$Cost=24.75\times 2=Rs. 49.50$

The parameter irrelevant for an electric fuse wire is 

physics electric current and its effects electric fuse electrical fuse and mcb fuse

  1. its radius.

  2. its specific resistance.

  3. current flowing through it.

  4. its length.

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Correct Option: D
Explanation:

For fuse wire expression for heat produced is given by eq. is  $H = \dfrac{I^2 \rho}{2 \pi ^2r^3}$
Hence, it is independent on length of fuse wire. Thus, the parameter irrelevant for an electric fuse wire is its length.