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Last-minute Physics doubts, SOLVED!

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March 25, 2009

Confused students posed their queries to Topper Science expert Leena Garg, during a live chat on March 25. And here's the transcript with all the answers!

Sanket Wani: Hi Maam. What is the resistance offered by a fuse, an ammeter and a voltmeter?
Leena Garg: Resistance of a fuse depends on the fuse wire. Resistance of an ammeter is ideally zero and that of a voltmeter is ideally infinity.

Neha: Hello Maam. Could u tell me that why the principal axis is always perpendicular to the mirror at its pole?

Leena Garg: That is how it is drawn, because by definition the principal axis is the line along which the ray of light passes through undeviated. Refer to What's HOTS?

Sanket Wani: What type of questions can be asked on the topic "Heating effects of electric current"?

Leena Garg: Practice numerical and learn the units well. Also learn the conversion of units. Practice by solving past exam papers.

Neha: Why does a convex mirror have a wider field of view?

Leena Garg: Because of its diverging nature.

Deepitapai: Can you please tell me as to how i should find the resistance in a circuit diagram when resistors are connected in different shapes & it becomes difficult to find out if they are connected in series or parallel.....many reference books give such questions, can such questions come in board exam?

Leena Garg: The only way out is to practice questions. You can refer to  What's HOTS?, Mock Papers, Solved board exam papers.

Sanket Wani : Ma'am, I am not able to apply the right hand thumb rule to a circular loop.Please help me.

Leena Garg: Right Hand Thumb Rule Imagine the conductor to be held in your right hand with the fingers curled around it. If the thumb points in the direction of the current, then the curled fingers show the direction of the magnetic field. Practice Mock Papers.

Gurman Bhatia: I basically face problems in questions regarding application of flemmings left hand and right hand rule. How can I overcome this problem?

Leena Garg: First of all remember, that you use the left hand rule when you have to find the direction of motion of the conductor. You use right hand rule to find direction of current. Just think of some memory mnemonic to remember this. Like say LM or left hand rule for motor.

Ahmed: What is 1 dioptre?

Leena Garg: 1 dioptre is the power of lens having 1 m focal length.

Monisha: Hi. Could you please tell me what will happen if the 3rd component from the left fails to work in a series circuit where the current is from left to right?

Leena Garg: I cannot understand your question without a diagram. If I have guessed correctly, you have 3 resistors connected in series. If the resistor fails the circuit will be discontinuous and current will stop flowing.

Creative: Is resistance provided by a fuse, an ammeter and a voltmeter?

Leena Garg: Resistance of ammeter and voltmeter is such that they do not affect the current in the circuit. Refer to Mock papers.