Electric Current And Its Effects(7th Grade > Physics ) Questions and answers for exam Preparation

7th Grade > Physics

ELECTRIC CURRENT AND ITS EFFECTS MCQs

Total Questions : 113 | Page 12 of 12 pages

Mention five differences between an electromagnet and permanent magnet. [5 MARKS]

Discuss Question

Answer: Option A. ->
:

Each point: 1 Mark
$\begin{matrix} E l e c t r o m a g n e t & P e r m a n e n t m a g n e t 1. I t i s a t e m p o r a r y m a g n e t a n d c a n b e d e m a g n e t i z e d & 1. I t i s a p e r m a n e n t m a g n e t a n d c a n n o t b e d e m a g n e t i z e d e a s i l y 2. M a g n e t i c s t r e n g t h c a n b e c h a n g e d & 2. I t s s t r e n g t h i s f i x e d 3. I t s p o l a r i t y c a n a l s o b e c h a n g e d & 3. I t s p o l a r i t y i s f i x e d 4. I t i s p r e p a r e d f r o m s o f t i r o n & 4. I t i s p r e p a r e d f r o m h a r d s t e e l 5. D i r e c t i o n o f m a g n e t i c f i e l d c a n b e r e v e r s e d & 5. D i r e c t i o n o f m a g n e t i c f i e l d c a n n o t b e r e v e r s e d 6. M a g n e t i c f i e l d i s p r o d u c e d w h e n e l e c t r i c c u r r e n t f l o w s . & 6. E l e c t r i c c u r r e n t i s n o t r e q u i r e d t o p r o d u c e m a g n e t i c f i e l d . \end{matrix}$

Question 112.

What are the various components of an electric bell? Explain the working of an electric bell. [5 MARKS]

Discuss Question

Answer: Option A. ->
:
Components: 2 Mark
Working: 3 Marks
An electric bell consists of a coil of wire. An electromagnet wound on an iron piece. The coil acts as an electromagnet.
An iron strip with a hammer at one end is kept close to the electromagnet. There is a contact screw near the iron strip.
When the iron strip is in contact with the screw, current flows through the coil which becomes an electromagnet.
It, then, pulls the iron strip. In the process, the hammer at the end of the strip strikes the gong of the bell to produce a sound.
However, when the electromagnet pulls the iron strip, it also breaks the circuit. The current through the coil stops flowing and it is no longer an electromagnet. It no longer attracts the iron strip.The iron strip comes back to its original position and touches the contact screw again.
This completes the circuit. The current flows in the coil and the hammer strikes the gong again.
This process is repeated in quick succession. The hammer strikes the gong every time the circuit is complete. This is how the bell rings.

What Are The Various Components Of An Electric Bell? Explain...

Question 113.

(a) Will the bulb glow in the circuit shown in Fig.? Explain. If not, what can be done to light the bulb?

(b) What happens when a bulb gets fused ?
[5 MARKS]

Discuss Question

Answer: Option A. ->
:
Part (a) : 3 Marks
Part (b): 2 Marks
(a) No, the bulb will not glow in this circuit because the switch is open and the circuit is incomplete.
Whenever we have an open circuit no current flows through it.
So, to light the bulb we can complete the circuit by putting any conductor connecting the two terminals.
We can use a metallic wire to close the open circuit. When we put a metallic wire the bulb will light up.
(b) When a bulb gets fused, its filament is broken that breaks the circuit and the flow of current stops.
The filament is made up of wire with high melting point like tungsten.
A filament is part of the light bulb that produces light.