BASIC SCIENCE FOR CLASS 7 AMARNATH MISHRA,PHD GEETA MEHTA ,PHD DEEPTI LEHRI,PHD RAJESH MOHAN, PHD
Physic
Ch -7
Electricity
A. Answer the following question in not more than 20 words
Only answer
1. A voltage difference.
2. The resistance of the filament in the bulb causes it to heat up.
3. This shows that a current-carrying conductor produces a magnetic field.
4. The nail becomes magnetized and aligns itself with the magnetic field of the coil.
5. A soft iron core is used in an electromagnet because it is easily magnetized and demagnetized.
6. Four devices that use the heating effect of electric current are:
* Electric heaters
* Electric stoves
* Electric irons
* Toasters
7. Four applications of electromagnets are:
* In motors
* In loudspeakers
* In relays
* In MRI machine
B. Answer the following question in not more than 40 words.
Only answer
1. A circuit diagram is a graphical representation of an electrical circuit. It shows the components of the circuit and how they are connected.
3. The heat produced by an electric current is proportional to the square of the current and the resistance of the circuit.
4. A long and thin tungsten filament is used in a bulb because it has a high resistance. This means that it will heat up more when an electric current passes through it.
5. Two problems associated with the heating effect of electric current are:* Fire: If an electric current passes through a material that is not a good conductor of heat, it can cause the material to heat up and catch fire.* Overheating: If an electric current passes through a material that is a good conductor of heat, it can cause the material to overheat and damage the circuit.
6. An electromagnet is a device that uses electricity to create a magnetic field. It is made up of a coil of wire that is wrapped around a metal core. When an electric current passes through the coil, it creates a magnetic field around the core.
Two properties of an electromagnet are:* It can be turned on and off by turning on and off the electric current.* The strength of the magnetic field can be increased by increasing the amount of current that passes through the coil.
C. Answer the following question in not more than 100 words.
Only answer
1. Electrical resistance is the opposition to the flow of electric current. It is measured in ohms. The resistance of a piece of material depends on its length, cross-sectional area, and the type of material. Resistance affects current by limiting the amount of current that can flow through a circuit.
2. A fuse is a safety device that is used to protect electrical circuits from damage caused by excessive current. It consists of a thin wire that melts when the current through it exceeds a certain value. This breaks the circuit and prevents damage to the equipment.
3. An electric bell is an electromechanical device that produces an audible sound when an electric current is passed through it. It consists of a coil of wire, a hammer, and an anvil. When the current is turned on, the coil creates a magnetic field that attracts the hammer. The hammer strikes the anvil, producing a sound. The sound is then amplified by the bell's housing.Here is a diagram of an electric bell:The bell consists of a coil of wire, a hammer, and an anvil. The coil is connected to a battery and a switch. When the switch is closed, current flows through the coil, creating a magnetic field. The magnetic field attracts the hammer, which strikes the anvil. The sound is then amplified by the bell's housing.
D. Fill in the blanks.
1. The greater the voltage across a device, the greater is the current through it.
2. The connections between components are represented by lines in a circuit diagram.
3. A long wire has more resistance than a short wire.
4. Overcurrent is a condition in which a wire carries a current that is more than what is safe.
5. A tightly wound length of wire is called a coil.
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