Derivation of formula for heat produced

Q.

An electric iron of resistance $20\Omega$ takes a current of $5A$. Calculate the heat developed in $30s.$

Q.

What do you mean by $H=I^{2}RT$?

Q.

Name any two effects of electric current.

Q.

An electric current of 3 A passes through a wire of resistance $15\Omega$ . How much heat will be developed in 1 minute?

Q.

What is Joule’s heating effect? How can it be demonstrated experimentally? List its four applications in daily life.

Q. A bulb can't be used in place of a resistor to verify Ohm's law. Why?

Q.

What is the expression for Joules law of heating?

Q.

An electric current can produce

1. heating effect only.

2. chemical effect only.

3. magnetic effect only

4. chemical, heating, and magnetic effects

Q.

What are the disadvantages of the heating effect of current?

Q.

(a) At what voltage is the electric power from the generating station transmitted? Give a reason for your answer.

(b) What is the nature of the current transmitted from the power station?

Q. 43.A large metal sheet carries an electric current along its surface . Current per unit lenght is (lamba). Find magnetic field induction near metal sheet is

Q.

Two conducting wires of the same material and of equal lengths and equal diameters are first connected in series and then in parallel with an electric circuit. The ratio of the heat produced in series and parallel combinations would be:

Q.

The rate of heat generated by electric current in a resistive circuit is expressed in

1. $IR$

2. $I{R}^2$

3. $I^{2}R$

4. $\sqrt{IR}$

Q. Filaments are present in bulbs.

1. incandescent
2. CFL
3. LED
4. all types of

Q.

How does the heat produced in a wire or a conductor depend upon the current passing through the conductor?

Q.

The resistance of a conductor is reduced to half its initial value. In doing so the heating effects in the conductor will become

1. half

2. double

3. one-fourth

4. four times

Q.

The laws of heating are given by _____________

Q.

Two conducting wires of the same material and of equal lengths and equal diameters are first connected in series and then in parallel in an electric circuit. The ratio of the heat produced in series and parallel combinations would be: [3 MARKS]

Q. Assertion :An electric bulb becomes dim, when the electric heater in parallel circuit is switched on. Reason: Dimness decreases after sometime.

1. Both Assertion and Reason are correct and Reason is the correct explanation for Assertion
2. Both Assertion and Reason are correct but Reason is not the correct explanation for Assertion
3. Assertion is correct but Reason is incorrect
4. Both Assertion and Reason are incorrect

Q.

Work function of a metal is

1. Minimum amount of energy required to start emission of electrons from the inside of the metal

2. Maximum amount of energy required to start emission of electrons from the inside of the metal

3. Maximum amount of energy required to start emission of electrons from the surface of the metal

4. Minimum amount of energy required to start emission of electrons from the surface of the metal

Q.

Figure show a simplified version of a device known as an lectron gun inside a cathode ray tube, X is a cathode which is heated by means of an electric current in the filament F. Y is a metallic hollow cylinder. F is connected to the terminals T1 and T2, X to the terminal T3 and Y to the terminal T4. What is the utility of 'F' and 'X'?

1. When current is passed through ‘F’ it gets heated up and transmits the heat energy to ‘X’ which is the anode and this anode accelerates the electrons

2. When current is passed through ‘F’ it gets heated up and transmits the heat energy to ‘X’ which is the cathode and this cathode emits the thermions using this thermal energy

3. When current is passed through ‘F’ it emits electrons and ‘X’ which is the cathode accelerates the electrons

4. When current is passed through ‘F’ it gets heated up and emits electrons. It then transmits the electrons to ‘X’ which is the anode and this anode accelerates the electrons

Q.

What do you think electrical energy actually is? For what do you pay your electricity bill?

Q. If a high power heater is connected to electric mains then the bulbs in the house become dim, becuase there is a

1. Current drop
2. Potential drop
3. No current drop
4. No Potential drop

Q.

Why does an electrical light or a bulb dont last forever thay have a particular lifetime approximately its several years why dont they last longer what is the reason behind this what causes the lifespan of the bulb to decrease?

Q. When a current flows through a conductor its temperature

1. May increase or decrease
2. Remains same
3. Decreases
4. Increases

Q. Assertion :The temperature of a metal wire rises when an electric current is passed through it. Reason: Collision of metal atoms with each other releases heat energy.

1. Both Assertion and Reason are correct and Reason is the correct explanation for Assertion
2. Both Assertion and Reason are correct but Reason is not the correct explanation for Assertion
3. Assertion is correct but Reason is incorrect
4. Both Assertion and Reason are incorrect

Q. Heat produced in a resistor when current is passed through it depends upon-

1. None of these
2. Current only
3. Time only
4. Current and time

Q. What do you understand by the thermal effect of electric current?

Q.

State the Principles behind working of HOT CATHODE RAY TUBE.

1. i) Thermionic emission ii) Electric and Magnetic fields cannot deflect electrons iii) Scintillation

2. i) Thermionic emission ii) Electric and Magnetic fields can accelerate and deflect electrons iii) Scintillation

3. i) Thermionic emission ii) Electric and Magnetic fields can accelerate and deflect electrons iii) oxidation

4. i) Photoelectric effect ii) Electric and Magnetic fields cannot accelerate electrons iii) Scintillation

5. i) Photoelectric effect ii) Electric and Magnetic fields can accelerate and deflect electrons iii) oxidation

Q. Give examples where we find heating of electric current.