# Tag: physics

### Questions Related to physics

Thermal energy produced by the resistance R in time duration 1 $\mu s$. using the source at resonance condition is

1. 0 J

2. $1 \mu J$

3. $100 \mu J$

4. not possible to calculate from the given information.

Correct Option: D

Current through resistor of resistance $R$ varies with time as $I = I _ot$. What will be the time taken to deliver heat $H$ by this resistor?

1. $\left( \cfrac { H } { I _ { 0 } R } \right) ^ { 1 / 2 }$

2. $\left( \cfrac { H } { 3 I _ { 0 } ^ { 2 } R } \right) ^ { 1 / 3 }$

3. $\left( \cfrac { 3 H } {I _ { 0 } ^ { 2 } R } \right) ^ { 1 / 3 }$

4. $\left( \cfrac { H } { I _ { 0 } ^ { 2 } R } \right) ^ { 1 / 3 }$

Correct Option: C

If p.d. across a conductor is constant and resistivity of its material is $\rho$, the joule heat produced in 1 s is proportional to ..

1. $\dfrac{1}{\rho }$

2. $\dfrac{1}{{\sqrt \rho }}$

3. $\rho$

4. ${{\rho ^2}}$

Correct Option: A

A coal based thermal power plant producing electricity operates between the temperatures $27^o C$ and $227^o C$ The plant works at 80% of its maximum theoretical efficiency. Complete burring of 1 kg of coal yields 3600 KJ of heat. A house needs 10 units of electricity each day. Coal used for supplying the amount of energy for the house in one year is

1. 1141 kg

2. 580 kg

3. 605 kg

4. 765 kg

Correct Option: B

Two equal resistance when connected in series to a battery, consume electri power  of 60 w.  If these resistnce are now  connected in parallel combination to  the same battery the electric power consumed will be

1. 60 W

2. 240 W

3. 30 W

4. 120 W

Correct Option: C

The formula used to calculate the heat produced in a conductor is

1. $H = IR^2 t$

2. $H= IRt$

3. $H = I^2Rt$

4. $H= VI$

Correct Option: C

Commonly used heating element are made of:

1. Iron

2. Manganese

3. Nichrome

4. Platinum

Correct Option: C
Explanation:

Because, alloy of nickel and chromium has high resistivity,

Why filament of electric bulb is made of tungsten

1. Melting Point of filament is very high

2. Resistance of filament is very less

3. Both

4. None

Correct Option: A
Explanation:

The resistance of filament should be high so that it can produce heat and light and its melting point should also be high so that it does not melt at the high temperature at which it is producing light.

The operating temperature of the filament of lamp is ${ 2000 }^{ 0 }C$. The temperature coefficient of the material of filament is ${ 0.005 }^{ 0 }{ C }^{ -1 }$. If the atmospheric temperature is ${ { 0 }^{ 0 }C }$, then the current in the 100W-200W lamp when it is switched on is nearest to

1. 2.5 A

2. 3.5 A

3. 4.5 A

4. 5.5 A

Correct Option: C

Which is not different between primary and secondary cell ?

1. Reversibility of chemical reaction

2. Rechargability of cell

3. Supply of energy to external circuit

4. Strength of current

Correct Option: C
Explanation:

Both primary and secondary cells serve the purpose of supplying energy to external circuit. Chemical reactions are reversible and cell is rechargeable for only secondary cells.  Strength of current in primary cell is low and in secondary cell can be high or low.