Physics [2 Mark Question Answer]

The ratio of number of turns NS in secondary coil to the number of turns NP in the primary coil (NS / NP) is called the turns ratio.
A transformer cannot be used with direct current (d.c.) since its working is based on the principle that when there is a change of magnetic field lines due to varying current of same in one coil, an induced varying current of same frequency flows in the other coil. If the current in one coil is constant (i.e. d.c.), no induced current will flow in the other coil since there will be no change in the magnetic field lines linked with the coil.

Features which provide greater efficiency to a transformer are:
(i) The core of the transformer is laminated which prevents the formation of eddy currents.
(ii) A closed soft-iron core is used which reduces the magnetic field link loss and hysteresis loss.

(a) We will observe that the needle of the galvanometer instantly jumps to one side and just as quickly returns to zero, indicating a momentary current in coil connected to galvanometer.
(b) Introducing an iron bar in the tube, will increase the amount of induced current and the galvanometer will show a greater deflection.

An ammeter is a low resistance device; hence it is connected in series.
A voltmeter is a high resistance device; hence it is connected in parallel.

A moving coil galvanometer can be converted into an ammeter by connecting a low resistance (called a shunt) in parallel to the galvanometer.
A moving coil galvanometer can be converted into a voltmeter by connecting a high resistance in series with the galvanometer.

(a) (i) When the magnet is moved rapidly in the direction of arrow, the magnetic flux linked with the coil changes and there is a deflection in the galvanometer, indicating a flow of current through the coil.
(ii) On keeping the magnet still, the magnetic flux linked with the coil does not change and there is no deflection in the galvanometer, indicating that no current is flowing through the coil.
(iii) When the magnet is rapidly pulled out, there is again change in the magnetic flux linked with the coil and the galvanometer shows a deflection but this time in opposite direction, indicating that a current is flowing in opposite direction in the coil.
(b) If a more powerful magnet is used, deflection in the galvanometer will be large, indicating a greater amount of current.

Fuse and switches are always connected to the live wire so that when the switch is in off position no current flows through the app lia nee and its live and neutra I wires are at same potential. In case, excess current flows through the I ive wire, the fuse wire me Its and breaks the circuit; so no excess current flows through the appliance and it is protected against any dam age.

Advantages of a parallel connection are:
(i) In parallel arrangement, each appliance works at the same voltage. For example, if several bulbs are connected in parallel, each bulb glows at the same voltage. Therefore, the glow of a bulb is unaffected if another bulb is switched on or off.
(ii) In parallel arrangement, if one bulb (or appliance

The ring system consists of a ring of three wires namely live wire, earth wire and neutral wire, which originate from the main fuse box and after running around the rooms in the house comes back to the main fuse box, thus, completing a ring. In ring system, a separate connection is taken from the live wire of the ring for each appliance. In the ring circuit, all appliances are connected in parallel.

Solution is as follow:

Incorrect statement:
(a) A 13A fuse is the most appropriate value to use

Replacing a fuse with another fuse of higher rating wou Id al low a large current to flow through the circuit or applia nee to which the fuse is connected and thus, there is a chance of short-circuiting and the appliance may get damaged.

An electric fuse is a device which is used to Ii m it the current in an electric circuit. The use of a fuse thus safeguards the circuit and appliances connected in that circuit from being damaged. It is a short piece of wire made of an alloy of lead and tin. If the current passing through the fuse exceeds the safeguard Ii m it the heat produced melts the fuse and this breaks the circuit.

Fleming's right hand rule can be stated as: Stretch the forefinger, the middle finger and the thumb of the right hand, such that they are mutually perpendicular to each other. If the forefinger indicates the direction of the magnetic field, thumb indicates the direction of motion of conductor, then the middle finger indicates the direction of induced current in the conductor.

E is for earth pin, N is for neutral pin and L is for live pin.
The earth pin is long so that the earth connection is made first. This ensures the safety of the user because if the appliance is defective, the fuse will blow off. The earth pin is made thicker so that even by mistake it cannot be inserted into the hole for the live or neutral connection of the socket.
The pins are splitted at the ends to provide spring action so that they fit in the socket holes tightly.

Earthing is a safety device which is used to prevent shocks due to short-circuiting and leakages. Earthing, means that the metal body of an appliance, or the kWh meter of the house, is connected to a thick copper wire which is buried deep in the earth and at its end ia a copper plate surrounded by a mixture of charcoal and common salt. This prevents the users from getting shocks.

According to this rule, stretch the thumb, forefinger and middle finger of your left hand such that they are mutually perpendicular. If the first finger points in the direction of magnetic field and the second finger in the direction of the current, then the thumb will point in the direction of motion of the conductor or the force acting on the conductor.

Fleming's right hand rule can be stated as: Stretch the forefinger, the middle finger and the thumb of the right hand, such that they are mutually perpendicular to each other. If the forefinger indicates the direction of the magnetic field, thumb indicates the direction of motion of conductor, then the middle finger indicates the direction of induced current in the conductor.

This is done to protect the appliances and circuits from any damage due to short-circuit and thus accidents like fire and fatal shocks. Earthing provides an easy and safe path to the excess current in the circuit and sends it to the ground.

An electric fuse is a device which is used to limit the current in an electric circuit. The use of a fuse thus safeguards the circuit and appliances connected in that circuit from being damaged. It is a short piece of wire made of an alloy of lead and tin. If the current passing through the fuse exceeds the safeguard limit the heat produced melts the fuse and this breaks the circuit.

Earthing is a safety device which is used to prevent shocks due to short-circuiting and leakages. Earthing, means that the metal body of an appliance, or the kWh meter of the house, is connected to a thick copper wire which is buried deep in the earth and at its end ia a copper plate surrounded by a mixture of charcoal and common salt. This prevents the users from getting shocks.

Precautions while using electricity:
(i) One must use wires or cables of current carrying capacity higher than the current which can flow through the circuit while using all appliances.
(ii) An electrical appliance must never be operated (or touched) with wet hands.

Short circuiting occurs when the live wire comes in direct contact with the neutral wire so a zero resistance path is provided to the current. The heavy current then passes through the appliance and wires of the circuit.

An electric fuse is a safety device which is used to limit the current in an electric circuit. The use of a fuse thus safeguards the circuit and appliances connected in that circuit from being damaged.
A fuse is generally made of an alloy of lead and tin.

Given, power P =720 w= 0.72 kW
Voltage, V = 220 volt
(a) Electrical energy consumed in 3 h = 0.72 x 3 = 2.16 kWh
(b) Cost of energy consumption @60 paise per kWh= 2.16 x Rs 0.6 =Rs 1.3

Electrical power is defined as the rate at which energy is changed or work is done i.e., the work done per second or energy converted per second.
Electrical appliances come with certain number of watts and volts written on them. Power rating of an electrical appliance gives the knowledge of the safe current limit of an appliance and also indicates the voltage above which the appliance should not be used.

Characteristics of fuse wire:
(i) It should have low melting point.
(ii) It should have high resistance.

The metal case of an electrical appliance is earthed so that in any case of accidental contact of live wire with the metallic body of the appliance, the earthing would provide a safe and easy path for the electric charges to flow down to the earth which acts as very large sink. Thus, user is thereby protected from any fatal electric shock.

A switch should not be touched with wet hands. If water reaches the live wire, it forms a conducting layer between the hand and the live wire of the switch through which the current passes to the hand and the person may get a fatal shock.

A switch is an on-off device for current in a circuit (or in an appliance). Its main function is either to connect or to disconnect an electrical appliance in an electric circuit.
Switches are always connected in the live wire of circuits so that when a switch is in 'off' position, no current flows through the appliance and its live and neutral wires are at same potential and it is safe to touch the live wire leading to the appliance, even when the fuse is blown.

Power-voltage rating of an electrical appliance indicates the value of voltage above which the appliance should not be used. It serves as a precaution to the customer and also helps to calculate the maximum value of current that can be safely passed through the appliance.

The SI unit of electrical energy is joule.
The SI unit of electrical power is watt.
(i) Kilowatt-hour is the household unit of electrical energy. It is defined as the quantity of electrical energy consumed in 1 hour when the rate of consumption is 1000 watts, i.e. 1000 J/s.
(ii) A voltage of 220 volt is generally supplied to a house.

One may get an electric shock from an electrical appliance if accidentally the live wire comes in contact with the metallic case of the body of the appliance due to break of insulation after constant use (or otherwise).

Earthing is done to save an electrical circuit or an appliance from damage. If due to some reason such as short circuiting, an excessive current flows through the line wires, it will pass to the earth if there is local earthing, otherwise it may cause a fire due to overheating of line wires.