Question

if the radii of two concentric circles are r1 and r2 (r1,7,r2) if r1-r2 =5 the the area between circle is​

Answer 1

Answer:

Step-by-step explanation:

Correct option is

B

r  

1

​

r  

2

​

 

r  

2

​

−r  

1

​

 

​

 

4π

ρ

​

 

Given,  

Radii of the concentric sphere s, r  

1

​

 and r  

2

​

           [r  

1

​

<r  

2

​

]

Resistivity of the material=ρ

As we know,  

Resistance can be given by the formula,  

R=ρ  

A

l

​

 

In this case,

length of the resistor here it's radius, l=r

and Area of the spherical resistor, A=4πr  

2

 

∴R=ρ  

4πr  

2

 

dr

​

 

[where r is any radius and dr is small element]

Total resistance,

R=  

4π

ρ

​

∫  

r  

1

​

 

r  

2

​

 

​

 

r  

2

 

dr

​

 

⇒R=  

4π

ρ

​

[−  

r

1

​

]  

r  

1

​

 

r  

2

​

 

​

 

⇒R=  

4π

ρ

​

[  

r  

1

​

 

1

​

−  

r  

2

​

 

1

​

]

⇒R=[  

r  

1

​

r  

2

​

 

r  

2

​

−r  

1

​

 

​

]  

4π

ρ

​

Answer 2

Hope it is helpful to you.