- Mention any two reasons of using nichrome wire in electric heater.
Any two reasons of using nichrome wire in electric heater are mentioned
- It has very high resistance as well as high melting point.
- It does not react with oxygen at air even at higher temperature about 900°C.
- A permanent magnet cannot be used in the electric bell. Why?
A permanent magnet cannot be used in the electric bell because of the
- It requires to have immediate magnetization and demagnetization in electrical bell.
- But it cannot be done in case of permanent magnet.
- Write two uses of transformer.
Two uses of transformer are:
- It is used to run machines in factories.
- It is used in power station, power sub-station.
- Why inert gas is filled in filament bulb?
- When the filament comes in contact with oxygen at high temperature, it gets destroyed due to oxidation. Therefore, inert or inactive gas such as argon, neon or nitrogen is filled in the filament lamp.
- Why is filament of tungsten metal used in filament lamp?
- Tungsten metal is used in filament because it has high resistivity and the high melting point of about 3400°C.
- The efficiency of any transformer is not 100%, why?
- The efficiency of any transformer is not 100% because the transformer windings have some resistance so some power is lost in heat when the current is flowing. These losses are proportional to the current flow.
- Write any two difference between generator and electric motor.
Any two difference between generator and electric motor is shown below in
Generator Electric motor It is a device which is used to produce electricity in a large scale. It is a device which converts electrical energy into mechanical energy. It works on the principle of electromagnetic induction. It works on the principle of motor effect.
- Write a reason to use soft iron core in a transformer.
- The reason to use soft iron core in a transformer is to prevent the loss of energy in the form of heat.
- Write two differences between primary coil and secondary coil in a step-up transformer on the basis of their structure.
- Number of turns in primary coil and secondary coil are different. Primary coil has fewer turns than secondary coil in step-up transformer.
- A current carrying conductor is placed in a magnetic field experiences a force, why?
- When a current carrying conductor is placed in a strong magnetic field there is regular attraction and repulsion of magnetic poles of two magnets by which current carrying conductor shows vibration. So, current carrying conductor is placed in a magnetic field experiences a force.
- On what principle does the bicycle dynamo work? Write two differences between primary coil and secondary coil in a step-down transformer on the basis of their structure.
Dynamo works on the principle of electromagnetic induction.
The number of turns in the primary coil and secondary coil are different. The primary coil has more turns than the secondary coil in a stepdown transformer. When current passes to the transformer, the primary coil absorbs more voltage, but the secondary coil absorbs less voltage.
- The tube of fluorescent lamp is filled with mercury vapor. Why?
- The tube of fluorescent lamp is filled with mercury vapor because it emits ultraviolet radiation that produces visible light when it strikes the fluorescent surface.
- Which metal is used as a filament? Why?
- Tungsten metal is used in filament because it has high resistivity and high melting point about 3400°C.
- State the principle of transformer. Why the core of transformer is laminated?
Transformer is based on the principle of mutual induction that is, when an
alternating current is passed in one coil then induced current is produced
in the neighboring coil.
The core of transformer is laminated with varnish and shellac so that it can prevent the flow of eddy current.
- Write any one difference in the construction of step up and step-down transformer.
- Primary coil has fewer turns than secondary coil in step-up transformer. Similarly, primary coil has more turns than secondary coil in stepdown transformer.
- From the given copper, nichrome and tungsten wire, choose the most suitable for each of the following.
- The heating element of an electric heater.
- The filament of an electric bulb.
- Tungsten wire
- Write the difference between electric motor and dynamo.
The difference between electric motor and dynamo are shown below in table:
Electric motor Dynamo It is a device which converts electrical energy into mechanical energy. It is a device which convert mechanical energy into electrical energy. It works on the principle of motor effect. It works on the principle of electromagnetic induction.
What type of transformer is shown in the diagram? Write one use of that type
Step up transformer is shown in the diagram. It is used in electric power
stations to distribute the AC voltage for a long distance.
More info: Don't count the number of rotations in either sides while making picture. Just observe which has comparatively more or less rotations.
- Write the formula to find out electric power consumption. In which effect of electricity is an electric bell based?
The formula to find out electric power consumption is:
Electric power consumption = power of electric appliance × number of appliances × time.
An electric bell is based in magnetic effect of electricity.
- What happens to the magnitude of induced electromotive force (emf) in an electric generator if the speed of rotor is doubled?
- If the speed of rotor is doubled then the magnitude of induced electromotive force (emf) will also be doubled because when the rotor rotates in high speed then the rotor along with magnet also spins in high speed. Then, the rate of coil that cuts the magnetic lines of force is also increased and more voltage is gained.
- Write four ways of increasing electricity produced from a generator or a dynamo.
Methods for increasing the amount of current produced by a generator or a
- Increasing the number of turnings of the coil.
- Using magnet with strong magnetic field.
- Increasing the speed of rotation of the coil.
- Reducing the distance between magnet and the coil.
- Write two difference between generator and dynamo.
Two difference between generator and dynamo are shown below in table:
Generator Dynamo It is used to operate many electrical devices. It is used to operate a signal device at a time. It is more powerful. It is less powerful.