| 10th Chapter: Electricity and its effects |
| Very Short Answer Questions 1 mark each with answers |
| Q.1 What is represented by joule/coulomb? |
| Answer. It represents potential difference. |
| Q.2 A charge of 2C moves between two plates, maintained at a p.d of 1V. What is the energy acquired by the charge? |
| Answer. W=QV=2×1=2J |
| Q.3 Why are copper wires used as connecting wires? |
| Answer. The electrical resistivity of copper is low |
| Q.4 A wire of resistivity 10 ohm meter is stretched to double its length. What is its new resistivity? |
| Answer. It remains same because resistivity depends on nature of material. |
| Q.5 What is the resistance of connecting wire? |
| Answer. The resistance of a connecting wire, which is made of good conductor, is negligible. |
| Q.6 What should be the resistance of an ammeter? |
| Answer. The resistance of an ammeter should be very small and for an ideal ammeter, its value is zero. |
| Q.7 What should be the resistance of a Voltmeter? |
| Answer. The resistance of a voltmeter should be very high and for an ideal voltmeter, its value is infinity. |
| Q.8 Which has more resistance: 100W bulb or 60W bulb? |
| Answer. As R is inversely proportional to P for constant V. Thus, the resistance of 60W bulb is more. |
| Q.9 How will you join three resistances, each of 2 ohm so that the effective resistance is 3 ohm? |
| Answer. A parallel combination of two resistances (which will be 1 ohm) joined in series with the third resistance (2 ohm) |
| Q.10 What happens to the current in a circuit if its resistance is doubled? |
| Answer. As I inversely proportional to R, the current is reduced to half of its previous value. |
| Q.11 What happens to the resistance of a circuit if the current through it is doubled? |
| Answer. The resistance of the circuit does not depend on the current through it., it will remain the same. |
| Q.12 How does the resistance of a wire depend upon its radius? |
| Answer. As R is inversely proportional to A, R is inversely proportional to square of radius r. |
| Short Answer Questions 2 mark each with answers |
| Q.1. Two wires are of the same length, same radius, but one of them is of copper and the other is of iron. Which will have more resistance? |
| Answer.A and l are same R depends only on resistivity and it is more for iron so iron has more resistance. |
| Q.2. Two wires of same material and same length have radii r1 and r2. Compare their resistances. |
| Answer. R inversely proportional to square of radius r. R1/R2 =(r2/r1)2 |
| Q.3. Given n resistors each of resistors Rs. How will you combine them to get the |
| ( i ) maximum and |
| (ii) Minimum effective resistance? What is the ratio of the maximum to minimum resistance? |
| Answer. (i)For maximum resistance Rs= nr (Equivalent of series combination) |
| (ii)For minimum resistance Rp= r/n (Equivalent of parallel combination) Rs/Rp= n2 |
| Q.4. A wire of length L and resistance R is stretched so that its length its doubled. How will its (a) Resistance change (b) Resistivity change ? |
| Answer. (a) If the original length of the wire is l and its cross-sectional area is A, then |
| R = l/A. When length becomes 2l, cross-sectional area reduces to A/2 because |
| volume does not change. The new resistance =(2l)/A/2=4 l/A = 4R |
| (b) Resistivity does not change |
| Q.5. How much work is done in moving a charge of 3 coulumb from a point at the volts 115 to a point at 125 volts? |
| Answer. Potential difference V= 125 - 115=10 volts Charge Q = 3 coulumb |
| V= W/Q W=Vx Q 10x3= 30 Joules. |
| Q.6. Ammeter burns out when connected in parallel. Give reasons. |
| Answer. Ammeter consists of a wire of low resistance when connected in parallel, a large amount of current passes through it hence gets burnt i.e. short circuited. |
| Related search and topics : |
Physics adda,cbse physics,CBSE NCERT sample paper,CBSE test paper ,CBSE NCERT Physics Notes,class 6th ,7th,8th ,9th,10th.
22 June 2011
10th Electricity very short and short questions answers
13 June 2011
10 June 2011
QUESTION BANK Class 9th Physics (Forces and Laws of motion)
CBSE PHYSICS Class IX ASSIGNMENT Forces and Laws of motion)
- What do you mean by a force?
- Give an example of a balanced force?
- Can force change the shape of an object? Give an example to prove your point?
- Do action and reaction force react in the same direction?
- Why a moving ship does takes longer time as compared to a car when equal breaks are applied?
- Why are passengers through in forward direction when a running bus stops suddenly?
- Why do passengers tend to fall sideways when the bus takes a sharp u turn?
- Why should a passenger hold on to prevent himself from swaying in a turning bus?
- Why do passengers tend to fall back when it starts suddenly?
- Why do passengers jumping out of a rapidly moving bus fall forward with his face downwards, if he does not run forward?
- Why does a passenger jumping out of a rapidly moving bus fall forward with his face downwards?
- Why can dust be removed by shaking it, or beating it by a carpet?
- Why does a bullet when fired against a glass window pane make a hole in it, and the glass pane will smash it?
04 June 2011
9th Forces and Laws of motion teat paper
Forces and Laws of motion teat paper
- Why do passengers tend to fall sideways when the bus takes a sharp u turn?
- Why should a passenger hold on to prevent himself from swaying in a turning bus?
- Why do passengers tend to fall back when it starts suddenly?
- Why do passengers jumping out of a rapidly moving bus fall forward with his face downwards, if he does not run forward?
- Why does a passenger jumping out of a rapidly moving bus fall forward with his face downwards?
- Why can dust be removed by shaking it, or beating it by a carpet?
- Why does a bullet when fired against a glass window pane make a hole in it, and the glass pane will smash it?
- Why does an athlete take a longer jump if he comes running from a distance than when he jumps suddenly from the take-off line?
- What happens when you shake a wet piece of cloth? Explain, why?
- Why is it advised to tie a rope on the luggage while you travel by the bus?
- How does a boat move forward into the water when the boatman presses one end of the pole against the ground?
- Why is it difficult for a fireman to hose, which ejects large amount of water at a high velocity?
Numerical Forces and Laws of motion
CBSE PHYSICS
Q. 1. How much force is needed to accelerate a trolley of mass 20g through 1 m/s2.
Q. 2. A force of 100N acts on a mass of 25 kg for 5 s .What velocity does it generate?
Q. 3. A bullet leaves a rifle with a velocity of 100m/s and the rifle of mass 2.5 kg recoils with a
velocity of 1m/s. Find the mass of the bullet?
Q. 4. A certain force acting on a mass of 15kg for 3s, gives it a velocity of 2m/s. Find the
magnitude of force.
Q. 5. A cricket ball of mass 0.15 kg is moving with a velocity of 1.2m/s . Find the impulse on the
ball and average force applied by the player if he is able to stop the ball in 0.18s.
Q. 6. A motor car of mass 200kg is moving with a certain velocity . It is brought to rest by the application of brakes, within a distance o f 20m when the average resistance being offered to it is 500N.What was the velocity of the motor car?
Q. 7. A body of mass 0.5kg undergoes a change of velocity of 4cm/s in 4s What is the force
acting on it?
Q. 8. A force of 8N acting on an 8kg mass for 4s provides its some velocity.Calculate the velocity
Q. 9. What would be the weight of a body of mass 50kg on the surface of the moon, where g = 1.6m/s2 what would be its mass?
Q. 10. A boy jumps a distance of 2m on the surface of the earth. What distance will he jump on the surface of the moon where g is 1/6th of the value on the surface of the earth?
Q. 11. Two bodies of mass 1kg and 2 kg moving in the direction opposite to each other with a speed 5m/s collide. Calculate the total momentum of the system before collision.
Q. 12. A bullet of mass 15g leaves the barrel of a gun with a velocity of 120m/s.The gun recoils with a velocity of 1m/s. Find the mass of the gun.
Q. 13. A force of 3N acts on a mass of 0.5kg at rest for 10s. Find the final velocity and the momentum of the body after 10s.
Q. 14. A force of 80N acting on a certain mass for 3s gives it a velocity of 6m/s. find the mass of the body if the body was initially at rest.
03 June 2011
ncert solution Force and Law of motio for class 9
Force and Laws of Motion (Science IX)
Which of the following has more inertia: (a) a rubber ball and a stone of the same size?
(b) a bicycle and a train? (c) a five-rupees coin and a one-rupee coin?
Inertia of an object id directly related the mass of the body. The greater is the mass of the body; the greater is its inertia and vice-versa.
when we vigorously shake the branches of a tree , it moves a tree to and fro, but its leaves try to remain at rest and fall down. In this case the inertia of the leaves tend to resist the to and fro motion of tree .
It is difficult for a fireman to hold a hose, which ejects large amounts of water at a high velocity due to the backward force applied by ejected water
When a fireman holds a hose, which is ejecting large amounts of water at a high velocity, then a reaction force is exerted on him by the ejecting water in the backward direction. This is because of Newton’s third law of motion. As a result of the backward force, the stability of the fireman decreases. Hence, it is difficult for him to remain stable while holding the hose.
An object experiences a net zero external unbalanced force. Is it possible for the object to be travelling with a non-zero velocity? If yes, state the conditions that must be placed on the magnitude and direction of the velocity. If no, provide a reason.
When the bus accelerates and moves in forward direction. The luggage kept on the roof try to retain its state of rest and ultimately falls from the roof of the bus and vice versa. Hence, to avoid this situation , it is advised to tie any luggage kept on the roof of a bus with a rope.
A batsman hits a cricket ball which then rolls on a level ground. After covering a short distance, the ball comes to rest. The ball slows to a stop because
(a) the batsman did not hit the ball hard enough.
(b) velocity is proportional to the force exerted on the ball.
(c) there is a force on the ball opposing the motion.
(d) there is no unbalanced force on the ball, so the ball would want to come to rest.
(c) A batsman hits a cricket ball, which then rolls on a level ground.there is frictional force on the ball opposing its motion.Hence, after covering a short distance, the ball comes to rest
You remember that frictional force always acts in the direction opposite to the direction of motion of object.
Two objects, each of mass 1.5 kg are moving in the same straight line but in opposite directions. The velocity of each object is 2.5 m s−1 before the collision during which they stick together. What will be the velocity of the combined object after collision?
Which of the following has more inertia: (a) a rubber ball and a stone of the same size?
(b) a bicycle and a train? (c) a five-rupees coin and a one-rupee coin?
Inertia of an object id directly related the mass of the body. The greater is the mass of the body; the greater is its inertia and vice-versa.
(a) Mass of a stone is more than the mass of a rubber ball for the same size.
Hence, inertia of the stone is greater than that of a rubber ball.
Hence, inertia of the stone is greater than that of a rubber ball.
(b) Mass of a train is more than the mass of a bicycle.
Hence, inertia of the train is greater than that of the bicycle.
Hence, inertia of the train is greater than that of the bicycle.
(c) Mass of a five rupee coin is more than that of a one-rupee coin. Hence, inertia of the five rupee coin is greater than that of the one-rupee coin.
In the following example, try to identify the number of times the velocity of the ball changes:
“A football player kicks a football to another player of his team who kicks the football towards the goal. The goalkeeper of the opposite team collects the football and kicks it towards a player of his own team”. Also identify the agent supplying the force in each case.
“A football player kicks a football to another player of his team who kicks the football towards the goal. The goalkeeper of the opposite team collects the football and kicks it towards a player of his own team”. Also identify the agent supplying the force in each case.
The velocity of the ball changes four times.
When a football player kicks the football, its speed changes from zero to a certain value. In this case, force applied by player helps to change the velocity of the ball. This at first changes the velocity of the ball.
Another player kicks the ball towards the goal post. This changes the direction of the ball . Therefore, its velocity also changes. In this case, the player applied a force to change the velocity of the ball. The goalkeeper collects the ball. In other words, the ball comes to rest. Thus, its speed reduces to zero from a certain value. The velocity of the ball has changed 2nd time
The goalkeeper applied an opposite force to stop/change the velocity of the ball. Hence, its velocity changes third time.
The goalkeeper kicks the ball towards his team players. Hence, the speed of the ball increases from zero to a certain value. Hence, its velocity changes once again. In this case, the goalkeeper applied a force to change the velocity of the ball.
Explain why some of the leaves may get detached from a tree if we vigorously shake its branch.Another player kicks the ball towards the goal post. This changes the direction of the ball . Therefore, its velocity also changes. In this case, the player applied a force to change the velocity of the ball. The goalkeeper collects the ball. In other words, the ball comes to rest. Thus, its speed reduces to zero from a certain value. The velocity of the ball has changed 2nd time
The goalkeeper applied an opposite force to stop/change the velocity of the ball. Hence, its velocity changes third time.
The goalkeeper kicks the ball towards his team players. Hence, the speed of the ball increases from zero to a certain value. Hence, its velocity changes once again. In this case, the goalkeeper applied a force to change the velocity of the ball.
when we vigorously shake the branches of a tree , it moves a tree to and fro, but its leaves try to remain at rest and fall down. In this case the inertia of the leaves tend to resist the to and fro motion of tree .
Why do you fall in the forward direction when a moving bus brakes to a stop and fall backwards when it accelerates from rest?
Ans: In a moving bus, a passenger moves with the bus due to inertia of motion. As the driver applies brakes, the bus comes to rest. But, the passenger tries to maintain to inertia of motion. As a result, a forward force is exerted on him.
Similarly, the passenger tends to fall backwards when the bus accelerates from rest. This is because when the bus accelerates, the inertia of rest of the passenger tends to oppose the forward motion of the bus. Hence, the passenger tends to fall backwards when the bus accelerates forward.
If action is always equal to the reaction, explain how a horse can pull a cart.Similarly, the passenger tends to fall backwards when the bus accelerates from rest. This is because when the bus accelerates, the inertia of rest of the passenger tends to oppose the forward motion of the bus. Hence, the passenger tends to fall backwards when the bus accelerates forward.
A horse pushes the ground with foot in the backward direction. According to Newton
Explain, why is it difficult for a fireman to hold a hose, which ejects large amounts of water at a high velocity.It is difficult for a fireman to hold a hose, which ejects large amounts of water at a high velocity due to the backward force applied by ejected water
When a fireman holds a hose, which is ejecting large amounts of water at a high velocity, then a reaction force is exerted on him by the ejecting water in the backward direction. This is because of Newton’s third law of motion. As a result of the backward force, the stability of the fireman decreases. Hence, it is difficult for him to remain stable while holding the hose.
Yes. Even when an object experiences a net zero external unbalanced force, it is possible that the object is traveling with a non-zero velocity.
This is possible only when the object has been moving with a constant velocity in a particular direction. Then, there is no net unbalanced force applied on the body. The object will keep moving with a non-zero velocity due to inertia of motion.
To change the state of motion, a net non-zero external unbalanced force must be applied on the object.
When a carpet is beaten with a stick, dust comes out of it. Explain.
This is possible only when the object has been moving with a constant velocity in a particular direction. Then, there is no net unbalanced force applied on the body. The object will keep moving with a non-zero velocity due to inertia of motion.
To change the state of motion, a net non-zero external unbalanced force must be applied on the object.
When a carpet is beaten with a stick, dust comes out of it. Explain.
When a carpet is beaten with a stick, then the carpet comes to motion. But, the dust particles try to resist their inertia of rest and the dust particles come out of the carpet.
Why is it advised to tie any luggage kept on the roof of a bus with a rope?
Why is it advised to tie any luggage kept on the roof of a bus with a rope?
When the bus accelerates and moves in forward direction. The luggage kept on the roof try to retain its state of rest and ultimately falls from the roof of the bus and vice versa. Hence, to avoid this situation , it is advised to tie any luggage kept on the roof of a bus with a rope.
A batsman hits a cricket ball which then rolls on a level ground. After covering a short distance, the ball comes to rest. The ball slows to a stop because
(a) the batsman did not hit the ball hard enough.
(b) velocity is proportional to the force exerted on the ball.
(c) there is a force on the ball opposing the motion.
(d) there is no unbalanced force on the ball, so the ball would want to come to rest.
(c) A batsman hits a cricket ball, which then rolls on a level ground.there is frictional force on the ball opposing its motion.Hence, after covering a short distance, the ball comes to rest
You remember that frictional force always acts in the direction opposite to the direction of motion of object.
Two objects, each of mass 1.5 kg are moving in the same straight line but in opposite directions. The velocity of each object is 2.5 m s−1 before the collision during which they stick together. What will be the velocity of the combined object after collision?
Mass of one of the objects, m1 = 1.5 kg
Mass of the other object, m2 = 1.5 kg
Velocity of m1 before collision, v1 = 2.5 m/s
Velocity of m2, moving in opposite direction before collision, v2 = −2.5 m/s
(Negative sign arises because mass m2 is moving in an opposite direction)
After collision, the two objects stick together.then Total mass = m1 + m2
Velocity of the combined object = v
According to the law of conservation of momentum:
Total momentum before collision = Total momentum after collision
m1v1 + m2 v1 = (m1 + m2) v
1.5(2.5) + 1.5 (−2.5) = (1.5 + 1.5) v
3.75 − 3.75 = 3 v
v = 0
Hence, the velocity of the combined object after collision is 0 m/s.and they comes into rest.
9th force and law of motion Test paper
9th Force and laws of motion Time 1 hr. M.M. 30
Answer the following questions: (carrying one marks each)
1. Define balance and unbalance force.
2. What is the usual name of force which can’t produce the motion but only change in shape?
3. What is the total moment of bullet and gun before firing?
4. Why are road accidents at high speed very much worse than accidents at low speed?
5. A body of mass 25 kg has a momentum of 125 kg m/s. calculate the velocity of the body.
6. Define 1N force.
7. write the relationship b/w force and acceleration.
8. A gun man gets a jerk on firing a bullet why?
9. State the low of conservation of momentum.
10. Explain the case of hose pipe.
(Carrying two marks each)
1. A bullet of mass 10 gm moving with a velocity of 400 m/sec gets embedded in a freely suspended wooden block of mass 900 gm. Calculate the velocity of wooden block acquired.
2. If action is always equal to reaction, explain why a cart pulled by a horse can be moved.
3. A truck started from rest and rolls down a hill with constant acceleration it travel a distance of 400 m in 20 sec. find its acceleration and force acting on it if the mass of the truck is 1 metric tones.
4. Explain the Newton’s second law of motion.
5. Why we use seat belts in car?
(carrying five marks each)
1. A man throws a ball weighing 500 gm vertically upwards with the speed of 10 m/sec find:
(a) What will be its initial momentum?
(b)What would its momentum at the highest point?
2. The velocity of a body of mass 10 kg increases form 4 m/sec to 8 m/sec When a force act on it for 2 sec. find
(a) What is the momentum before the force act?
(b)What is the momentum after the force act?
(c) What is the momentum gain in momentum per sec.
(d)What is the value of force?
Answer the following questions: (carrying one marks each)
1. Define balance and unbalance force.
2. What is the usual name of force which can’t produce the motion but only change in shape?
3. What is the total moment of bullet and gun before firing?
4. Why are road accidents at high speed very much worse than accidents at low speed?
5. A body of mass 25 kg has a momentum of 125 kg m/s. calculate the velocity of the body.
6. Define 1N force.
7. write the relationship b/w force and acceleration.
8. A gun man gets a jerk on firing a bullet why?
9. State the low of conservation of momentum.
10. Explain the case of hose pipe.
(Carrying two marks each)
1. A bullet of mass 10 gm moving with a velocity of 400 m/sec gets embedded in a freely suspended wooden block of mass 900 gm. Calculate the velocity of wooden block acquired.
2. If action is always equal to reaction, explain why a cart pulled by a horse can be moved.
3. A truck started from rest and rolls down a hill with constant acceleration it travel a distance of 400 m in 20 sec. find its acceleration and force acting on it if the mass of the truck is 1 metric tones.
4. Explain the Newton’s second law of motion.
5. Why we use seat belts in car?
(carrying five marks each)
1. A man throws a ball weighing 500 gm vertically upwards with the speed of 10 m/sec find:
(a) What will be its initial momentum?
(b)What would its momentum at the highest point?
2. The velocity of a body of mass 10 kg increases form 4 m/sec to 8 m/sec When a force act on it for 2 sec. find
(a) What is the momentum before the force act?
(b)What is the momentum after the force act?
(c) What is the momentum gain in momentum per sec.
(d)What is the value of force?
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