State two ways to increase the speed of rotation of a D.C. motor.

State two ways to save energy.

State two ways to prevent the rusting of iron.

The best way to increase the yield of crop :-

State two ways to minimise the impact of global warming.

When does a body rotate? State one way to change the direction of rotation of the body. Give a suitable example to explain your answer.

What energy change takes place in a dc motor ? On what principle does it work? State one factor to increase its speed of rotation.

A uniform metallic rod rotates about its perpendicular bisector with constant angualr speed. If it is heated uniformly to raise its temperature slightly, then a) its speed of rotation increases b) its speed of rotation decreases c) its speed of rotation remains same d) its speed increases because its moment of inertia increases

A dc motor works on the principle that a current carrying coil, when placed in a magnetic field experiences a torque. The arrangement consists of a coil suspended in a region of magnetic field. When a current is passed through the coil, it experiences torque and starts rotating. A simple arrangement is shown below. The coil rotates under the action of torque. The current is supplied to the coil by an arrangement of two sliding contacts and a split ring. As the coil rotates, the magnetic flux linked with the coil changes. This leads to production of an induced emf epsilon in the coil. By Lenz's law, the induced emf opposes the applied voltage and therefore, it is called back emf. If R is the resistance in the coil, the current i flowing through the coil at any instant is i=(V-epsilon)/(R) . The back emf is developed due to induction and it is directly proportional to speed of rotation and it is directly proportional to speed of rotation of the motor. There is a continuous power loss i^(2)R in the motor, in form of heat. When a dc motor is running unloaded (full speed) the current through it is 1 A. What will be the current flowing through the motor, when it is loaded to run at half its maximum speed, it applied voltage is 10 V and armature resistance is 5 Omega

A dc motor works on the principle that a current carrying coil, when placed in a magnetic field experiences a torque. The arrangement consists of a coil suspended in a region of magnetic field. When a current is passed through the coil, it experiences torque and starts rotating. A simple arrangement is shown below. The coil rotates under the action of torque. The current is supplied to the coil by an arrangement of two sliding contacts and a split ring. As the coil rotates, the magnetic flux linked with the coil changes. This leads to production of an induced emf epsilon in the coil. By Lenz's law, the induced emf opposes the applied voltage and therefore, it is called back emf. If R is the resistance in the coil, the current i flowing through the coil at any instant is i=(V-epsilon)/(R) . The back emf is developed due to induction and it is directly proportional to speed of rotation and it is directly proportional to speed of rotation of the motor. There is a continuous power loss i^(2)R in the motor, in form of heat. In a dc motor, V is applied voltage, epsilon is back emf, i is current through the motor and R is resistance of the coil. mechanical power output of the motor is

A dc motor works on the principle that a current carrying coil, when placed in a magnetic field experiences a torque. The arrangement consists of a coil suspended in a region of magnetic field. When a current is passed through the coil, it experiences torque and starts rotating. A simple arrangement is shown below. The coil rotates under the action of torque. The current is supplied to the coil by an arrangement of two sliding contacts and a split ring. As the coil rotates, the magnetic flux linked with the coil changes. This leads to production of an induced emf epsilon in the coil. By Lenz's law, the induced emf opposes the applied voltage and therefore, it is called back emf. If R is the resistance in the coil, the current i flowing through the coil at any instant is i=(V-epsilon)/(R) . The back emf is developed due to induction and it is directly proportional to speed of rotation and it is directly proportional to speed of rotation of the motor. There is a continuous power loss i^(2)R in the motor, in form of heat. The mechanical power output of a dc motor is maximum, when the current through the motor is