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Fuse is always connected to live wire. If fuse wire is connected to the neutral wire instead of live wire then even when the fuse burns out, the appliance remains connected to the live wire and the current supply will not be disrupted due to overloading.

The earth pin is thicker so that it does not enter into the live or neutral sockets. It is longer so that the earth connection is made first. This ensures the safety of the users.

Uses of electromagnet are: –

I. It is used in motors and generators to change the magnetic flux linked with the coil and produce current.

II. It is used in transformers to alter the voltage by the phenomena of mutual induction.

(i) There is a deflection in galvanometer connected with coils, due to induced current.

(ii) Defleciion becomes zero.

(iii) Deflection in galvanometer is in opposite direction.

Reason:

(i) E.M. induction takes place because the field is changing.

(ii) Since current becomes stationary, no change in the field takes place. So no EM induction.

(iii) E.M. induction takes place but the induced current is in opposite direction.

the shape of a current-carrying conductor is  Solenoid.

A current-carrying wire concealed in a wall can be located due to the magnetic effect of current by using a plotting compass. If a plotting compass is moved on a wall, its needle will show deflection at the place where current-carrying wire is concealed.

A strong magnetic field produced inside a solenoid can be

Used to magnetize a piece of magnetic material, like soft iron, when placed inside the coil.

The magnet so formed is called an electromagnet.

Electromagnets are used in electric bells, loudspeakers, telephone diaphragms and electric fan.

Giant electromagnets are also used in cranes to carry materials in bulk.

Yes, we can change the polarity of an electromagnet by reversing the direction of the current. 

Uses of electromagnets :

(i) In electric bells

(ii) For separating magnetic substances such as iron and other metallic substances from metallic scrap.

The strength of an electromagnet can be increased by 

(i) increasing the number of turns in the coil 

(ii) increasing the current flowing in the coil 

(iii) reducing the length of air gap between the poles

Electromagnets are used in several electrical devices such as electric bell, electric motor, loudspeaker etc. They are also used by doctors to remove particles of iron or steel from a patient’s eye and to remove pieces of iron from wounds.

If the current in the wire is increased, the deflection increases. The strength of magnetic field is directly proportional to the magnitude of current passing through the straight conductor.

 Strength of electromagnet depends on:

i. The number of turns in the coil – Increasing the number of turns in the coil increases the strength of the electromagnet. 

ii. The current flowing in the coil – Increasing the current flowing in the coil increases the strength of the electromagnet. 

iii. The length of air gap between its poles: Reducing the length of air gap between the poles of electromagnet increases the strength of the electromagnet

 Core of an electromagnet should be of soft iron and not of steel because soft iron loses all its magnetism when current in the coil is switched off but steel does not lose its magnetism when the current is stopped.

Brain and heart.

The soft iron inside the coil makes the magnetic field 

Stronger because it becomes a magnet itself when the current is flowing. That is, Soft iron is said to form a temporary magnet. In this way, the electromagnet can be switched on and off by turning the electricity on and off.

The relationship between force and acceleration is the force acting on a body is directly proportional to the acceleration produced in the body.

According to Newton’s first law of motion, a body continues to remain in the state of rest or in the state of motion until an external force acts on it. Sliding of a book on the table is an example of Newton’s first law of motion.

(a) According to Newton’s third law of motion: Whenever one body exerts a force on another body, the second body exerts an equal and opposite force on the first body. In other words, to every action, there is an equal and opposite reaction. Two examples to illustrate this law- When a man jumps out from a boat, the boat moves backwards. This is due to the fact that to step out of the boat, the man presses the boat with his foot in the backward direction. The push of the man on the boat is action. The boat exerts an equal force in the forward direction and since the boat is not fixed and is floating, it moves backwards due to the action force exerted by the man. Gunman gets a jerk on firing a bullet from his gun. This is because when a bullet is fired from a gun, the force sending the bullet forward is equal to the force sending the gun backwards but due to high mass of the gun, it moves only a little distance backwards giving a jerk to the gunman. 

(b) When a fireman directs a powerful stream of water on a fire, the hose pipe tends to go backward due to the reaction force of the water rushing through it in the forward direction at a great speed.

Mass of the first object, m₁ = 1.5 Kg.
Mass of second object m₂ = 1.5 Kg.
Velocity of first object before collision, u₁ = 2.5 ms^-1
velocity of second object before collision, u₂ = -2.5 ms^-1
Here negative sign is taken because second object is moving in the direction opposite to the direction of motion of first object.
Mass of combined object after collision
M = m₁ + m₂ (Since they stick together)
= 1.5 + 1.5 = 3 Kg.
Let velocity of combined object after collision be vms^-2
Here there is no external force, so from law of conservation of momentum
Momentum after collision = Momentum before collision
mv = m₁u₁ + m₂u₂
3 × v = 1.5 × 2.5 + 1.5 (-2.5) =0
∴ v = 0.

Given, 

Force, F = 5N 

Mass, m = 10kg 

Acceleration, a = F/m = 5/10 

= 0.5 m/s²

The correct answer is c) 0.25

Acceleration remains same as a = F/m 

If the force is doubled then mass will also be doubled ie; 2F and 2m 

Then acceleration a = 2F/2m = F/m 

Therefore, acceleration remains the same.

(i) Rocket taking off from the ground: The chemicals inside the rocket burn and produce very high velocity blast of hot gases. These gases pass out through the tail nozzle of the rocket in the downward direction with tremendous speed and the rocket moves up to balance the momentum of the gases. The gases have a very high velocity ang hence a very large momentum. An equal momentum is imparted to the rocket in the opposite direction, so that it goes up with a high velocity. 

(ii) Flying of jet aeroplane: In jet aeroplanes, a large volume of gases produced by the combustion of fuel is allowed to escape through a jet in backward direction. Due to high velocity, the backward rushing gases have a large momentum. They impart an equal and opposite momentum to the jet aeroplane due to which it moves forward with a great speed.

This is an inherent property called inertia of rest which is directly proportional to the mass of the object. 

Examples: – 

1. When we beat carpet dust particles comes out. 

2. When you shake the branch of tree fruits or leaves comes out.

The physical quantity that corresponds to the rate of change of momentum is force.

The SI unit of momentum is kg.m/s.

Gunman gets a jerk on firing a bullet because when a bullet is fired from a gun, the force sending the bullet forward is equal to the force sending the gun backwards but due to high mass of the gun, it moves only a little distance backwards giving a jerk to the gunman.

Object B has more inertia. Since mass is a measure of inertia of a body and object B has greater mass, so it will have greater inertia.

Inertia of motion is the property of a body due to which it resists a change in its state of uniform motion. For eg., if there is no air resistance and no friction to oppose the motion of a moving bicycle, it will go on moving forever.

Slope in the velocity versus time graph is acceleration and hence it is due to application of force. 

a) The slope is constant, so the force is constant and is acting in the direction of motion. 

b) The force acting on the object is zero because there is no velocity change. 

c) The slope is constant, so the force is constant and is acting opposite to the direction of motion.

The total momentum of the bullet and the gun before firing would be zero because velocities of both of them will be zero.

Momentum is a vector quantity and is dirceted along the direction of velocity.

a) When the forces acting on a body is zero, the forces are called balanced force. Pressing of a balloon between both the hands is an example of balanced force. 

When the forces acting on a body is not zero, the forces are called unbalanced force. Pushing a toy car is an example of unbalanced force in which the car starts to move as there is unbalanced force acting on it. 

b) When a rubber ball is pressed between our hands, balanced force acts on it and therefore, there is no change in its shape.

The correct option is b) change in shape of the body

Balanced forces can change the shape of the object. For example, when a balloon is pressed between hands, then balanced forces (equal and opposite forces) act on the balloon due to which the shape of the balloon changes.

Mass of ball = 500 g = 0.5 kg

Initial velocity = 10 m/s

1. Initial momentum = 0.5 x 10 = 5 kg.m/s

2. Velocity at the highest point = 0 m/s

Momentum at the highest point = 0.5 x 0 = 0 kg.m/s

The wall will receive equal momentum from both the balls because both balls have equal mass and velocity.

In this case, the bicycle has been compelled to change its state of motion by the external force of air resistance and friction. If there were no air resistance and no friction to oppose the motion of the bicycle, then according to the first law of motion, the bicycle would go on moving forever.

The unbalanced force which slows down a moving bicycle when we stop pedaling is known as frictional force.

Balanced force cannot produce motion in a body but can only change the shape.