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How does use of a fuse wire protect electrical appliances?

Answer: An electrical fuse is a low melting point copper or other metal wire that breaks due to heat caused by overvoltage or high load to... View Article

Draw a circuit diagram of an electric circuit containing a cell, a key, an ammeter, a resistor of 2 Ω in series with a combination of two resistors (4 Ω each) in parallel and a voltmeter across the parallel combination. Will the potential difference across the 2 Ω resistor be the same as that across the parallel combination of 4Ω resistors? Give reason.

Answer: The effective resistance of the combination of two resistors in parallel is, Reff = (4 × 4)/(4 + 4) Reff = 16/8 Reff = 2Ω... View Article

Should the resistance of an ammeter be low or high? Give reason.

Answer: Resistance of ammeter should be zero because ammeter should not affect the flow of current. Ammeter is used to measure current. It... View Article

Three 2 Ω resistors, A, B and C, are connected as shown in Figure. Each of them dissipates energy and can withstand a maximum power of 18W without melting. Find the maximum current that can flow through the three resistors?

Answer: The maximum power each resistor can withstand is 18W. We know that P = I2 × R Where P - Power I - Current R - Resistance P =... View Article

A child has drawn the electric circuit to study Ohm’s law as shown in Figure. His teacher told that the circuit diagram needs correction. Study the circuit diagram and redraw it after making all corrections.

Answer: Ohm’s law states that the voltage across a conductor is directly proportional to the current flowing through it, provided all... View Article

Two resistors of resistance 2 Ω and 4 Ω when connected to a battery will have (a) same current flowing through them when connected in parallel (b) same current flowing through them when connected in series (c) the same potential difference across them when connected in series (d) different potential difference across them when connected in parallel

Answer: (b) same current flowing through them when connected in series In series, the combination current does not get divided into branches... View Article

An electric kettle consumes 1 kW of electric power when operated at 220 V. A fuse wire of what rating must be used for it? (a) 1 A (b) 2 A (c) 4 A (d) 5 A

Answer: (d) 5 A Given parameters Power (P) = 1 KW = 1000 W Voltage (V) = 220 V The maximum current that the appliance requires can be... View Article

In an electrical circuit, two resistors of 2 Ω and 4 Ω respectively are connected in series to a 6 V battery. The heat dissipated by the 4 Ω resistor in 5 s will be (a) 5 J (b) 10 J (c) 20 J (d) 30 J

Answer: (c) 20 J A circuit is said to be connected in series when the same amount of current flows through the resistors. In such circuits, the... View Article

In an electrical circuit, three incandescent bulbs A, B and C of rating 40 W, 60 W and 100 W respectively are connected in parallel to an electric source. Which of the following is likely to happen regarding their brightness? (a) The brightness of all the bulbs will be the same (b) The brightness of bulb A will be the maximum (c) The brightness of bulb B will be more than that of A (d) The brightness of bulb C will be less than that of B

Answer: (c) The brightness of bulb B will be more than that of A Bulbs are connected in parallel so the resistance of combination would be less... View Article

If the current I through a resistor is increased by 100% (assume that temperature remains unchanged), the increase in power dissipated will be (a) 100 % (b) 200 % (c) 300 % (d) 400 %

Answer: (c) 300 % Heat generated by a resistor is directly proportional to the square of the current. Hence, when the current becomes double,... View Article

A student carries out an experiment and plots the V-I graph of three samples of nichrome wire with resistances R1, R2 and R3 respectively. Which of the following is true? (a) R1 = R2 = R3 (b) R1 > R2 > R3 (c) R3 > R2 > R1 (d) R2 > R3 > R1

Answer: (c) R3 > R2 > R1 Slope for R1 is maximum and slope for R3 is the minimum. R1 slope > R2 slope > R3 slope We know that... View Article

Which of the following represents voltage? (a) Work done/(Current×Time) (b) Work done × Charge (c) (Work done×Time)/Current (d) Work done × Charge × Time

Answer: (a) Work done/(Current×Time) Voltage, also called electromotive force is simply the energy per unit charge. In other words, voltage is... View Article

The proper representation of the series combination of cells (Figure) obtaining maximum potential is (a) (i) (b) (ii) (c) (iii) (d) (iv)

Answer:(a) (i) Here positive terminal of the next cell is adjacent to the negative terminal of the previous cell. A circuit is said to be... View Article

What is the minimum resistance which can be made using five resistors each of 1/5 Ω? (a) 1/5 Ω (b) 1/25 Ω (c) 1/10 Ω (d) 25 Ω

Answer: (b) 1/25 Ω Minimum resistance is obtained when resistors are connected parallel. A circuit is said to be connected in parallel when the... View Article

What is the maximum resistance which can be made using five resistors each of 1/5 Ω? (a) 1/5 Ω (b) 10 Ω (c) 5 Ω (d) 1 Ω

Answer: (d) 1 Ω Maximum resistance is obtained when resistors are connected in series. A circuit is said to be connected in series when the... View Article

Identify the circuit in which the electrical components have been properly connected. (a) (i) (b) (ii) (c) (iii) (d) (iv)

Answer: (b) (ii) Checking to see if the Voltmeter and Ammeter are linked in parallel and series. Voltmeter is connected in series in... View Article

A current of 1 A is drawn by a filament of an electric bulb. Number of electrons passing through a cross-section of the filament in 16 seconds would be roughly (a) 10^20 (b) 10^16 (c) 10^18 (d) 10^23

Answer: (a) 1020 Given parameters I = 1 A t = 16 sec e = 1.6 × 10-19 C Current drawn by the filament can be calculated as I = Q/t Since... View Article

In the following circuits the heat produced in the resistor or combination of resistors connected to a 12 V battery will be (a) same in all the cases (b) minimum in case (i) (c) maximum in case(ii) (d) maximum in case(iii)

Answer: (c) maximum in case(ii) According to joule's law of heating, the heat produced due to the current is given by H = I2/Rt The... View Article

Draw the symbols of the following circuit components. (i) electric cell (ii) switch in off position (iii) electric bulb (iv) battery

Answer: (i) Electric cell An electric cell is a device, which converts chemical energy into electrical energy. It has two terminals, which are... View Article

How does the magnetic effect of electric current help in the working of an electric bell? Explain with the help of a diagram.

Answer: The electric doorbell is a simple circuit that triggers a sound on the completion of circuit by pressing the button. The working... View Article

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