Physics Help

[Saad Mughal]

Hello Everyone! Hope you are having a good time studying (unlike me) .
I needed help on the following contents of the syllabus:

• describe how heat is transferred to or from buildings and to or from a room.
• describe the relative order of magnitude of the expansion of solids, liquids and gases.

Any notes/explanations would be great. Thanks!

 

[kashaf shahzad]

I also have problem in the second part...please help...

 

[Saad Mughal]

I read in the Complete physics IGCSE book that water expands 7 times as much as steel and air expands 16 times as much as water but that won't suffice because that is not the relative magnitude of SOLID, LIQUIDS and GASES.

 

[Usama Jawad]

Hello Everyone! Hope you are having a good time studying (unlike me) .
I needed help on the following contents of the syllabus:

• describe how heat is transferred to or from buildings and to or from a room.
• describe the relative order of magnitude of the expansion of solids, liquids and gases.

Any notes/explanations would be great. Thanks!

1-Heat is transferred to or from buidings by convection and radiation.and in a room it is transferred by same methods(like convection curreants by AC or heaters) except if objects are in contact,heat is also transferred by conduction.
2-You dont need to know the relative order of magnitude of expansion according to Physics Syllabus,you just need to know that gases expand the most and solids the least.
Hope you find these helpful.

 

[Saad Mughal]

I figured these out from a reference book but Thanks anyway!
Although, I read that heat is transferred to buildings through convection currents and from the buildings through radiation and conduction (floor,ceiling,windows).

 

[Ashna Mungla]

Hi, please help i am confused about potential difference and electomotiveforce
i badly need help

 

[Saad Mughal]

Electromotive force is the work done per unit charge in driving charge around a complete circuit (in other words it is the energy converted from all other forms to electrical energy); it is measured by connecting the voltmeter in series with the circuit.
Potential difference is the work done per unit charge in driving charge through a COMPONENT (such as a resistor) (in other words, it is the energy converted from electrical energy to all other forms); it is measured by connecting the voltmeter in parallel (or across) the component.
That's all you need to know according to the syllabus. Hope that helps.

 

[Usama Jawad]

Electromotive force is the work done per unit charge in driving charge around a complete circuit (in other words it is the energy converted from all other forms to electrical energy); it is measured by connecting the voltmeter in series with the circuit.
Potential difference is the work done per unit charge in driving charge through a COMPONENT (such as a resistor) (in other words, it is the energy converted from electrical energy to all other forms); it is measured by connecting the voltmeter in parallel (or across) the component.
That's all you need to know according to the syllabus. Hope that helps.

Precisely Summarised,I would have explained it the same way

 

[Saad Mughal]

 

[Ashna Mungla]

Thanks

 

[Ashna Mungla]

Oops I need help on Total Internal Reflection

 

[Saad Mughal]

Refraction is projected at the surface of the medium (air) at an angle that is known as the angle of incidence, the refraction occurs after the light passes through the medium with a angle known as the angle of refraction. Now, we know that refractive index=constant=sin i/sin r, therefore, as i increases r increases, there comes a time when the angle of incidence produces a angle of refraction that is equal to 90, this means that the light does not pass through the medium but travels along its wall. This angle of incidence is at that point = critical angle which is the maximum angle at which refraction occurs, when moving from denser to lighter medium, the law of the angles reverses and it becomes, sin r/sin i=n where n is the refractive index of the denser medium, hence when angle of incidence = critical angle, it becomes sin 90/sin i = n , i=c, therefore, n=1/sin c.
This was all about critical angles, now, if we project the light ray at an angle greater than critical angle, the light rays reflect back since they cannot bend away, the reflected rays obey the laws of reflection and this reflection is known as total internal reflection. You can think of the phenomenon in this way that when a light ray is projected within a thick glass at an angle greater than critical angle, the glass acts like a plane mirror. Total internal reflection is used in optical fiber which transfer data very quickly through the reflection of light. Remember, Total internal reflection ALWAYS occurs from denser to lighter medium.
In short, critical angle is the maximum angle at which a light ray refracts (angle of refraction = 90), beyond the critical angle, the light ray does not refract instead it reflects back.
Hope that helps. P.S. I know, the drawing's poor

 

[Ashna Mungla]

Refraction is projected at the surface of the medium (air) at an angle that is known as the angle of incidence, the refraction occurs after the light passes through the medium with a angle known as the angle of refraction. Now, we know that refractive index=constant=sin i/sin r, therefore, as i increases r increases, there comes a time when the angle of incidence produces a angle of refraction that is equal to 90, this means that the light does not pass through the medium but travels along its wall. This angle of incidence is at that point = critical angle which is the maximum angle at which refraction occurs, when moving from denser to lighter medium, the law of the angles reverses and it becomes, sin r/sin i=n where n is the refractive index of the denser medium, hence when angle of incidence = critical angle, it becomes sin 90/sin i = n , i=c, therefore, n=1/sin c.
This was all about critical angles, now, if we project the light ray at an angle greater than critical angle, the light rays reflect back since they cannot bend away, the reflected rays obey the laws of reflection and this reflection is known as total internal reflection. You can think of the phenomenon in this way that when a light ray is projected within a thick glass at an angle greater than critical angle, the glass acts like a plane mirror. Total internal reflection is used in optical fiber which transfer data very quickly through the reflection of light. Remember, Total internal reflection ALWAYS occurs from denser to lighter medium.
In short, critical angle is the maximum angle at which a light ray refracts (angle of refraction = 90), beyond the critical angle, the light ray does not refract instead it reflects back.
Hope that helps. P.S. I know, the drawing's poor

View attachment 23395

Thank you a lot, no matter whether the drawing is poor i have understand it

 

[Saad Mughal]