At constant temperature, the current flowing through a conductor is directly proportional to the potential difference across its ends. Note: Ohm's law is given by: V = I R Where, V =Voltage I = Current R = Resistance

Write the name of two devices based on heating effect of electric current.

Bulb and an electric fuse are two devices that work on the heating effect of electric current. In an electric bulb, the filament is used to produce heat and light which should have high resistance and high melting point. Usually, tungsten is used to make filament. Fuse wire is used to protect a circuit from high currents. Fuse wire gets heated and melted and breaks the circuit when a large current flows through it.

Two electric bulbs A and B are marked 60 W , 220 V and 100 W , 220 V respectively. Which one of the two has greater resistance?

We know that, P = V 2 R Where P is power in Watt W , R is resistance in Ohm Ω , V is voltage in volts V . So, given a rating of bulbs are: 100 W , 220 V & 60 W , 220 V . Here, the potential is the same then P ∝ 1 R So, Power is inversely proportional to the Resistance if Voltage is the same. So, 60 W bulb resistance is greater than 100 W a bulb.

Explain the principle and working of electric motor, by drawing its labelled diagram.

Principle Of Electric Motor: Electric motor works on the principle that when a rectangular coil is placed in a magnetic field and current is passed through it. A force acts on the coil which rotates it continuously. The electric motor is a device that converts electrical energy to mechanical energy. Construction: An electric motor consists of a rotating rectangular coil ABCD placed between the two poles of a permanent magnet. The two conducting stationary brushes X and Y are kept pressed separately on the slip rings P and Q, respectively. These two rings are attached to an axle (the axle can be rotated mechanically). The outer ends of the two brushes are connected to the battery for the flow of current in the given circuit. Working: let the current flow through the coil ABCD. By applying Flemings' left-hand rule, an electric current is set up in the winding. Permanent magnets provide the magnetic field. In this case, current-carrying armature conductors experience a force due to the magnetic field, according to the principle stated above. The Commutator is made segmented to achieve unidirectional torque. Otherwise, the direction of force would have reversed whenever the direction of movement of the conductor is reversed in the magnetic field.

How much work is done in moving a charge of 5 C across two points having a potential difference 15 V ?

Given: Potential difference = 15 V , Charge = 5 C . Electric potential is the flow of charge from one conductor to another in contact. Potential difference = work done charge V = W Q By substituting the values, 15 = W 5 ⇒ W = 15 × 5 ⇒ W = 75 J . Hence, the amount of work done in moving a charge 5 C across two points is 75 J .

A Refrigerator of 400 W power is run for 8 hours/day. What will be the cost of the energy to operate it for 30 days? (Rate Rs. 3 . 00 per kwh )

Given: Power consumed by the refrigerator = P = 400 W The time taken to consume (per day) = t = 8 hours (i) To find cost, we need to find energy consumed in 30 days We know that, Power = Energy consumed Time taken E n e r g y c o n s u m e d = P o w e r × t i m e t a k e n = P × t = 400 × 8 = 3200 Wh = 3 . 2 kWh (ii) Finding energy consume in 30 days Energy consumed in 1 day = 3 . 2 kWh Energy consumed in 30 day = 30 × 3 . 2 = 96 kWh . (iii) Finding cost The cost of 1 kWh = Rs 3 The cost of 96 kWh = 96 × 3 = 288 Hence, the cost of energy consumption is Rs 288 .