All questions
- A horizontal overhead power line carries a current of 90 A in east to west direction. I = 90 A, r = 1.5 m B = fracμ₀ I2 π r = frac4 π × 10⁻⁷ × 902 π × 1.5 = 1.2 x 10⁻⁵ T (South) 1
- A long straight wire in the horizontal plane carries a current of 50 A in north to south direction. Give the magnitude I = 50 A, r = 2.5 m B = fracμ₀ I2 π r = frac4 π × 10⁻⁷ × 502 π × 2.5 = 4 x 10⁻⁶ T upwards. (due to the wire alone) 1
- A long straight wire carries a current of 35 A. What is the magnitude of the field B at a point 20 cm from the w ire? I = 35 A, r = 20 cm = 20 x 10⁻² m B = fracμ₀ I2 π r = frac4 π × 10⁻⁷ × 352 π × 20 × 10⁻² = 3.5 x 10^(-5 )T 1
- A circular coil of wire consisting of 100 turns, each of radius 8.0 cm carries a current of 0.40 A. n = 100, I = 0.40 A, r = 8.0 cm = 8.0 x 10⁻² m B = fracμ₀ nI2 r = frac4 π × 10⁻⁷ × 100 × 0.42 × 8 × 10⁻² = π x 10^(-4 )T 1
- What do you mean by the steady current? A steady current is that in which the intensity of current remains constant. 1
- What do you mean by the varying current? A varying current is the one in which the intensity of current does not remain constant. 1
- Why does current become a scalar quantity? Currently does not obey vector addition principle, i.e., the sum of currents always remains the same, whatever be the angle between conducto... 1
- The free electrons inside a metallic conductor are in random motion. Can we detect current in the conductor? No. In random motion, the average velocity is zero. 2
- What is the essential condition for current flow in a conductor? When a potential difference is applied across the conductor, an electric field is set up and electrons begin to make directed flow and hence... 1
- How can you produce a net flow of electric charges [electric current] in a conductor? By applying a p.d. Under the action of the electric field applied, electrons make drift motion and this produces current. 1
- In the electric field, what happens to the motion of the electrons? Electrons flow in a direction opposite to the electric field. 1
- Why is an ammeter connected in series and a voltmeter in parallel? Ammeter is a low resistance instrument. Hence if ammeter is put in series, it allows the entire current to flow through it and we can measur... 2
- What is the variation of resistivity with temperature? Resistivity, ρ = ρ₀(1 + α t) for conductors where ‘ α ’ is the temperature coefficient of resistance and ‘t’ the temperature change. So resi... 1
- What is superconductivity? In 1911, the Dutch Physicist, Kamerlingh Onnes established experimentally that certain metals and alloys lose their resistance at a very low... 1
- How can you define temperature coefficient of resistance? Temperature coefficient of resistance is defined as the ratio of increase in resistance to the original resistance per degree rise of temper... 1
- How can you compare the emf of two cells? Using potentiometer we can compare the emf of two cells. 2
- What is meant by the internal resistance of a cell? Internal resistance of a cell is defined as the resistance offered by the components inside it to the flow of current. The value of internal... 1
- If a person touches a live wire, will he get stuck to it? Why do we use copper wires as connecting wires? Sometimes. Even very small currents are enough to disorganise our nervous system. Hence the affected person may temporarily lose his ability... 1
- Light from a bathroom bulb gets dimmer for a moment when Geiser is switched on. Why? Since the resistance of the geiser is less than that of a bulb, geiser draws more current from the mains than the bulb. So the bulb becomes... 1
- In the above figure, the numbers 1, 2, 3 and 4 have got some meaning. (a) What is the meaning of each number? (a) The first coloured band (1) gives the first significant figure, second coloured band (2) gives second significant figure, third coloured... 1
- What is conventional current? The current which flows from the positive to negative end of a cell in the external circuit is called conventional current. 1
- What is the significance of the direction of the current? The direction of the conventional current is opposite to the flow of electrons. The direction of electronic current is in the direction of t... 1
- How does drift velocity of electrons in a metallic conductor vary with temperature? The drift velocity of electrons in a metallic conductor decreases with an increase in temperature. 1
- Why are connecting wires made of copper? Copper has very low resistivity (high conductivity). Also copper is a diamagnetic material, so it is not magnetised due to the flow of curre... 1