DELHI PUBLIC SCHOOL – ELECTRONIC CITY
PREBOARD EXAM I (2025-26)
SUBJECT: PHYSICS [042]
CLASS: XII MARKS: 70 Marks
DATE: __/__/25 DURATION: 3 Hours
NAME: ___________________________________ ROLL NO: ____________
MARKING SCHEME
Question # SOLUTION STEPS MARKS
SECTION A
Q1. (A) −21 𝑛𝐶 [1 Mark]
Q2. (A) Zero [1 Mark]
Q3. (C) 32 𝑛𝐴 [1 Mark]
Q4. (C) 6.0 × 10−7 𝑁𝑚−1; Repulsive [1 Mark]
Q5. (C) ΔΦ𝐵 = 250 𝑊𝑏 [1 Mark]
Q6. (A) 0𝑜 [1 Mark]
Q7. (D) Infra-red Rays [1 Mark]
Q8. (D) Interference [1 Mark]
Q9. (B) 3.0 𝑐𝑚 [1 Mark]
Q10. (D) Phase [1 Mark]
Q11. (A) λ𝐿𝑦,α : λ𝐵𝑎,α = 5: 27 [1 Mark]
Q12. (B) Boron [1 Mark]
Q13. (C) A is true but R is false. [1 Mark]
Q14. (A) Both A and R are true and R is the correct explanation of A. [1 Mark]
Q15. (B) Both A and R are true but R is not the correct explanation of A [1 Mark]
Q16. (D) A is false but R is true. [1 Mark]
, SECTION B
𝑞 𝑉1 𝑟1 [1 Mark]
𝑉1 = 𝑘 ; ⟹ 𝑞=
𝑟1 𝑘
Q17. (300 𝑉)(60 × 10−2 𝑚)
𝑞 = = 2.0 × 10−6 𝐶 = 2.0 μ𝐶 [1 Mark]
(9.0 × 109 𝑁𝑚2 /𝐶 2 )
(a) Mobility of a charge carrier depends on:
(i) the mass of the charge carrier,
(ii) temperature of the material.
(b) As the temperature increases the speed of random motion increases and the [1 Mark]
Q18.
relaxation time (τ) decreases. Resistivity is inversely proportional to the
relaxation time which is inversely proportional to the temperature. [1 Mark]
1 1
ρ∝ ; τ∝ ⟹ ρ∝𝑇
τ 𝑇
Hard Ferromagnets Soft Ferromagnets
Ferromagnetic materials in which Ferromagnetic materials in which
the magnetization persists even after the magnetization disappears upon [1 Mark]
the removal of external magnetizing the removal of external magnetizing
field are called Hard Ferromagnets. field are called Soft Ferromagnets.
o These are material with high o These are material with low
coercivity. coercivity.
Q19.
o These materials are used for o These materials are used for
making permanent magnets. making electromagnets and
transformer cores.
Examples: Alnico; Hard Ferrites, Examples: Pure Iron, Soft Iron,
Carbon steel; Lodestones. Soft Ferrites; Mu-Metals [1 Mark]
(a) Ampere’s circuital law was found to violate the charge conservation
principle. This problem was traced to the fact there exists a second mechanism [1 Mark]
for generating magnetic fields, besides electric current. Maxwell modified it
to accommodate the second mechanism of generating magnetic field.
Ampere’s Circuital Law:
⃗⃗⃗⃗ = μ0 𝐼𝑐
⃗ . 𝑑𝑟
∮𝐵
𝐶
𝐼𝑐 – Conduction Current
Maxwell-Ampere Law:
𝑑Φ𝐸
Q20. ⃗ . ⃗⃗⃗⃗
∮𝐵 𝑑𝑟 = μ0 (𝐼𝑐 + ϵ0 )
𝐶 𝑑𝑡
(b) Displacement Current: A time-varying electric flux produces a magnetic
field. Since electric current produces a magnetic field, a time varying electric
flux has the same effect as electric current and can be represented as an abstract
current called displacement current. [1 Mark]
𝑑Φ𝐸
∮𝐵 ⃗ . ⃗⃗⃗⃗
𝑑𝑟 = μ0 (𝐼𝑐 + ϵ0 ) = μ𝑜 (𝐼𝑐 + 𝐼𝑑 );
𝐶 𝑑𝑡
𝑑Φ𝐸
𝐼𝑑 = ϵ0
𝑑𝑡
PREBOARD EXAM I (2025-26)
SUBJECT: PHYSICS [042]
CLASS: XII MARKS: 70 Marks
DATE: __/__/25 DURATION: 3 Hours
NAME: ___________________________________ ROLL NO: ____________
MARKING SCHEME
Question # SOLUTION STEPS MARKS
SECTION A
Q1. (A) −21 𝑛𝐶 [1 Mark]
Q2. (A) Zero [1 Mark]
Q3. (C) 32 𝑛𝐴 [1 Mark]
Q4. (C) 6.0 × 10−7 𝑁𝑚−1; Repulsive [1 Mark]
Q5. (C) ΔΦ𝐵 = 250 𝑊𝑏 [1 Mark]
Q6. (A) 0𝑜 [1 Mark]
Q7. (D) Infra-red Rays [1 Mark]
Q8. (D) Interference [1 Mark]
Q9. (B) 3.0 𝑐𝑚 [1 Mark]
Q10. (D) Phase [1 Mark]
Q11. (A) λ𝐿𝑦,α : λ𝐵𝑎,α = 5: 27 [1 Mark]
Q12. (B) Boron [1 Mark]
Q13. (C) A is true but R is false. [1 Mark]
Q14. (A) Both A and R are true and R is the correct explanation of A. [1 Mark]
Q15. (B) Both A and R are true but R is not the correct explanation of A [1 Mark]
Q16. (D) A is false but R is true. [1 Mark]
, SECTION B
𝑞 𝑉1 𝑟1 [1 Mark]
𝑉1 = 𝑘 ; ⟹ 𝑞=
𝑟1 𝑘
Q17. (300 𝑉)(60 × 10−2 𝑚)
𝑞 = = 2.0 × 10−6 𝐶 = 2.0 μ𝐶 [1 Mark]
(9.0 × 109 𝑁𝑚2 /𝐶 2 )
(a) Mobility of a charge carrier depends on:
(i) the mass of the charge carrier,
(ii) temperature of the material.
(b) As the temperature increases the speed of random motion increases and the [1 Mark]
Q18.
relaxation time (τ) decreases. Resistivity is inversely proportional to the
relaxation time which is inversely proportional to the temperature. [1 Mark]
1 1
ρ∝ ; τ∝ ⟹ ρ∝𝑇
τ 𝑇
Hard Ferromagnets Soft Ferromagnets
Ferromagnetic materials in which Ferromagnetic materials in which
the magnetization persists even after the magnetization disappears upon [1 Mark]
the removal of external magnetizing the removal of external magnetizing
field are called Hard Ferromagnets. field are called Soft Ferromagnets.
o These are material with high o These are material with low
coercivity. coercivity.
Q19.
o These materials are used for o These materials are used for
making permanent magnets. making electromagnets and
transformer cores.
Examples: Alnico; Hard Ferrites, Examples: Pure Iron, Soft Iron,
Carbon steel; Lodestones. Soft Ferrites; Mu-Metals [1 Mark]
(a) Ampere’s circuital law was found to violate the charge conservation
principle. This problem was traced to the fact there exists a second mechanism [1 Mark]
for generating magnetic fields, besides electric current. Maxwell modified it
to accommodate the second mechanism of generating magnetic field.
Ampere’s Circuital Law:
⃗⃗⃗⃗ = μ0 𝐼𝑐
⃗ . 𝑑𝑟
∮𝐵
𝐶
𝐼𝑐 – Conduction Current
Maxwell-Ampere Law:
𝑑Φ𝐸
Q20. ⃗ . ⃗⃗⃗⃗
∮𝐵 𝑑𝑟 = μ0 (𝐼𝑐 + ϵ0 )
𝐶 𝑑𝑡
(b) Displacement Current: A time-varying electric flux produces a magnetic
field. Since electric current produces a magnetic field, a time varying electric
flux has the same effect as electric current and can be represented as an abstract
current called displacement current. [1 Mark]
𝑑Φ𝐸
∮𝐵 ⃗ . ⃗⃗⃗⃗
𝑑𝑟 = μ0 (𝐼𝑐 + ϵ0 ) = μ𝑜 (𝐼𝑐 + 𝐼𝑑 );
𝐶 𝑑𝑡
𝑑Φ𝐸
𝐼𝑑 = ϵ0
𝑑𝑡
